What would independence for Scotland actually mean in practice? As the political row over an independence referendum rumbles on – on what questions to ask, and when – Guardian commenters have been asking in their droves what would happen on several key day-to-day issues if Scotland voted "yes".

Commenter harbord summarised these questions nicely in a post below a previous Reality Check:

Will the terms of the independence be agreed before the vote? I'm not eligible to vote but if I was I would like to know details on matters such as defence, amount of debt that Scotland would inherit, currency, EU membership, etc. Without a prior agreement I can foresee Alex Salmond using the 'intransigence of the English' as a rallying call for the SNP in the 2015 general election when he is denied independence on terms that are highly favourable to Scotland, which he surely will demand

These questions are the subject of a special week-long series of Reality Checks, looking at the fate of sterling, oil revenues, and even the BBC.

Today – hopefully with your help – I'm tackling what independence might mean for Scotland's national debt, and just as importantly its potential deficit, and credit rating.

How much debt?

Firstly, a caveat: every single aspect of Scotland's postition post-referendum would be subject to doubtlessly intense political negotiations. As a result, any attempts to suggest figures beforehand are at best sensibly-derived estimates, and at worst, guesses.

That aside, a fairly simple way to look at how much debt an independent Scotland might have is to allocate Scottish people their "fair share" by capita of the UK's total debt pile.

The UK's national debt in January 2012 stood at £988.7bn – excluding bank bailouts, a topic to which we will return later.

Scotland's GDP per capita is only slightly below the UK's average (at 98.7% of the UK average), so it is a reasonable approximation to divide this debt evenly by population.

Scotland contains around 5.1 million of the UK's 62.2 million people, which would leave its share of the debt by this working at £81bn.

With UK debt projected to increase over the next five years to around 71% of GDP (it current stands at around 63%), this is very likely to rise.

What about the deficit?

Public sector debt of £81bn is a reasonably large amound for a small country like an independent Scotland, but not necessarily unmanageable. What is perhaps more important is the deficit.

The deficit is the gap between a country's income and its spending – a measure of how much further the government is going into debt each year. This can either be worked out using the current account (ignoring capital projects and other one-off factors), or all-in, which is referred to as "net borrowing" in official accounts.

Scotland's government has already worked out how these would compare to the UK average for 2009/10, in a first set of notional accounts for the country, which attempt to compare Scottish spending with revenue obtained from Scottish taxpayers. They're published in full here.

The accounts quickly reveal the huge importance of North Sea oil to the Scottish economy. This is the subject of a Reality Check later this week, so for now we will stick to the two scenarios outlined in the Scottish accounts.

One is a "per capita" share of oil revenues – giving Scotland around 9% of the proceeds of North Sea oil.

The other is a "geographical share" of oil revenues – which gives Scotland around 90% of North Sea oil revenues, though some dispute the geographical borders Scotland uses to calculate these.

Using the first scenario, Scotland's net borrowing is a parlous £19.3bn in 2009/10 – around 17% of GDP. Using the geographical measure, Scotland's net borrowing is £14bn, or 10.6% of GDP.

This difference is substantial: the UK's net borrowing for the year was 11.1%, so depending on how oil revenues are apportioned, Scotland's borrowing is either slightly less, or substantially more, than the nation as a whole.

The cost of borrowing

Such calculations rely on the assumption that Scotland could borrow for a similar cost to the UK government at present. The UK enjoys exceptionally low bond yields at present, thanks partly to its AAA credit rating, boosted by the effect of the Bank of England's substantial QE (which lowers bond yields).

Commentators have noted, however, that an independent Scotland might not receive so strong a rating. Notable among them is Martin Wolf in the FT (£) who argued:

According to the Scottish government, even with what it calls its "geographical share" of revenue from the North Sea, its overall fiscal position was a deficit of 10.6% of gross domestic product in 2009-10. Yet revenue from the North Sea is set to decline. Moreover, Scotland would presumably inherit a pro rata share of UK net public debt, forecast by the UK Treasury to peak at 71% of GDP in 2013-14. A newly independent small country with sizeable fiscal deficits, high public debt and reliance on a declining resource for 12% of its fiscal revenue, could not enjoy a triple A rating. Its costs of borrowing might be far higher than those of the UK. To avoid the risk, it would need to lower its debts quite rapidly. This would require even greater austerity than in the UK as a whole.

Missing something?

When calculating Scotland's debt, we used a measure which excluded liabilities obtained through the bank bailouts. Tends of billions were directly loaned to banks, and through guarantees and other deals, the UK as a whole is liable for hundreds of billions more.

The UK's net liabilities without including the banks is £988.7bn. Including them takes the total to around £2,200bn.

Two of the largest recipients of this state aid were the Royal Bank of Scotland and Halifax Bank of Scotland (HBOS, now taken over by Lloyds TSB).

I'll take a look at the debate over how these liabilities should be apportioned, and what this might mean for Scotland, in a later post.

Any insight of data on this issue – or anything else around Scottish public finances – would be gratefully received. As ever, you can contribute through the comments, via Twitter to @jamesrbuk, or through email to james.ball@guardian.co.uk.

Trading partners

Data on ways to split the liabilities of public sector banks is so far proving elusive: some take the view it should be split by customer base (which would be problematic given many Lloyds and RBS customers are outside the UK), while a certain school of thought feels Scotland should take the whole burden of RBS liabilities due to the bank's Scottish headquarters.

Neither feels to stretch much beyond opinion to me – so any data or evidence on how splits might work, and their potential consequences would be hugely welcome. Please do send links if so.

One useful thing to note is that if Scotland were to become independent, it would be in the interests of both countries to make sure it was a financially viable nation.

Analysis by Angus Armstrong of NIESR notes Scotland would be a very open economy: businesses owned by the rest of the UK account for around 20% of employment and turnover, with a further 16% coming from other international businesses.

Further evidence from Scotland's experimental data series were even more telling about the scale of the rest of the UK as a hugely significant trading partner:

Combining official and the Scottish government's experimental data series, the total value of exports and imports of goods and services, or all goods and services traded across Scotland's borders, is broadly the same as the value of output consumed within Scotland's borders. In economic terms, this implies that Scotland is a small and very open economy. The rest of the UK is comfortably Scotland's largest trading partner. Exports to the rest of the UK were equivalent to 40% of national output or more than 60% of total exports, ie more than exports to the rest of the world combined. Imports from the rest of the UK are an even larger proportion of output and imports from the rest of the world.

Such closely tied trading would suggest in the medium and long run, whatever debt settlements were agreed would have to be sustainable in both Scotland and the rest of the UK unless both were to suffer from significant loss of trade.

Ways to split the bank bailout

There's a lively discussion going on in the comments around the issues of debt division and credit ratings – particularly splitting bank debt – throwing up some heat but also a lot of light.



One particularly interesting and noteworthy point came from AnneDon who pointed out credit ratings need not necessarily be the be-all-and-end-all when it comes to debt levels:



One of the many points raised in Scottish Ministers' Question Time last week, and one of many which Michael Moore responded to with invective rather than an answer was this.



The UK has a AAA credit rating.

Japan has an AA- rating.



However, Japan pays a lower rate of interest than the UK because its economy is healthier.



Surely this is worth mentioning - credit ratings are not the be-all and end-all - it's the overall strength of the manufacturing base that matters.



And, as you've said, Scotland is an open economy, and the intention is to make it an export-driven one.





The issue of bank division is perhaps the most discussed issue (after oil, which is tackled in depth later this week – all this post has done is state two positions stated within the Scottish government's official accounts).



Hireton quotes the view of Professor Hughes Hallett on this issue:

"The real point here, and this is the real point, is by international convention, when banks which operate in more than one country get into these sorts of conditions, the bailout is shared in proportion to the area of activities of those banks, and therefore it's shared between several countries. In the case of the RBS, I'm not sure of the exact numbers, but roughly speaking 90% of its operations are in England and 10% are in Scotland, the result being, by that convention, therefore, that the rest of the UK would have to carry 90% of the liabilities of the RBS and Scotland 10%. And the precedent for this, if you want to go into the details, are the Fortis Bank and the Dexia Bank, which are two banks which were shared between France, Belgium and the Netherlands, at the same time were bailed out in proportion by France, Belgium and the Netherlands."





While this view has many supporters – and some examples in practice – it should be noted it's not the sole view, and has some eminent detractors too.



However, some comment has come through by email (and phone) from people within the City who feel a similar stance is practical. This view stems from the idea that there is in reality only at present a British framework for banking – including backstops, regulation, and ultimate fallbacks.



To this view, defining a bank as English or Scottish is likely a futile exercise. This reasoning would suggest splitting the UK's bank liabilities on a per-capita basis, as with debt.



This would leave Scotland with £81bn of public sector debt, and around a further £100bn of liabilities from the bank bailouts. Liabilities, it should be noted, largely represent guarantees against default extended by the UK government, rather than actual debt.



A final note from the same financial sources suggests the issue of Scotland's credit rating is as reliant on its currency as its debt. If Scotland were to enter a formal currency agreement with the rest of the UK to keep Sterling (a Euro-like agreement), it would be more likely to keep a AAA rating than if it were to establish a new currency, or use sterling without explicit agreements with the rest of the country.



We're still going – more evidence or opinions on the issue of Scotland's debt or deficit are welcome as ever.

Day one roundup

Right, we're going to round off the above-the-line posts on today's Reality Check here – but we'll keep the comments open for a while for responses to a few final questions.



Thanks to everyone for a really great comment thread – and one quick above-the-line clarification thanks to several commenters is to note the Spanish government has denied it would have any objection to an independent Scotland being a member of the EU.



It's also clear just how reliant the figures mooted in today's post and comments are influenced by the factors up for discussion during the rest of the week, so please feed in any evidence, data or useful information on those as the week goes on so we can build as thorough and fair a picture as possible of the effects of Scottish independence.

We're going to look at whether there's a good way to do a summary of the Reality Checks – including the information from the comments – over the week to make a more definitive round-up later, as suggested by a few people in the comment threads over the day.



One final request from me regards calls in the comments to look at the 1974 McCrone report and several postings from John Jappy, largely referring to evidence from the late 1990s.



I've neglected to incorporate these to a significant extent above-the-line due partly to their controversial nature, but mainly because in a post trying to look at current financial positions and projections (a complex enough endeavour), it seemed most appropriate to concentrate on the most recent evidence, from the Scottish government, NIESR, and elsewhere.



What's your thoughts on the best way to handle this older material – particularly when (as in this case) it's inclusion (or exclusion) is likely to prove controversial?

• This article was corrected on 28 February 2012 because it referred to the 1974 McCoy report, instead of the McCrone report.