An independent Scotland could expect to become a member of the European Union within 18 months of a yes vote, according to a senior EU negotiator.

Graham Avery, the European Commission's honorary director general, said the UK government's position on Scotland in Europe was "perplexing" and "absurd".

He also told a Holyrood committee the country could not be compelled to join the euro or Schengen travel area.

But pro-Union MSPs said Mr Avery's opinions had already been "ruled out".

Mr Avery, who was appearing before the European and External Relations Committee, negotiated the UK's entry into the European Community in the 1970s and wrote the membership applications of 14 countries.

He said voters should dismiss the UK government's anti-independence "tactics" and the "obscure" statements of European leaders which suggest and independent Scotland would face a difficult journey to EU membership.

'Reasonable solution'

He added: "I consider, along with Sir David Edward, that Article 48 would be applicable and I confidently predict that in the event of a yes vote the EU will consider whether to use it.

"If and when the result of the referendum is in favour of independence then it seems to me perfectly clear that the Westminster government and Whitehall machine will move into action very smartly to find a reasonable solution."

In its White Paper on independence, launched in November, the Scottish government said the country would look to gain membership through Article 48 of the Treaty of the European Union.

The UK government and pro-Union Better Together campaign have consistently rejected the claim that Scotland would get "accelerated" entry into the EU.

Last week, three eminent lawyers also challenged the SNP's claim, but were dismissed by former European Court judge Sir David Edward, who said the UK would have an "obligation" to secure Scotland's continuing membership, a view echoed by Mr Avery.

European Council president Herman van Rompuy and European Commission president Jose Manuel Barroso have previously said the EU treaties would not apply to any part of a member state that becomes independent from another.

Asked about these interventions, Mr Avery described what they had said as "not the whole truth".

He added that Scotland would not need to opt-out of the euro or the Schengen passport-free travel area because it could not be compelled to join them.

'No guarantees'

Conservative MSP Jamie McGrigor admitted Mr Avery had "superior knowledge on Europe" but Labour MSP Patricia Ferguson said his opinions had been "in effect ruled out" by the European Commission and came with no guarantees.

Blair Jenkins, chief executive of Yes Scotland, described the intervention as "an extremely significant and important contribution from an eminent and vastly-experienced European policy adviser".

"People can be reassured that an independent Scotland will remain a member of the European Union," he added.

A Better Together spokesperson said: "The notion that we could unpick a union that has lasted 300 years, set up an entirely new state, conclude negotiations on massive issues like debt and currency, and do what no other country has been able to do in terms of accelerated EU membership in 18 months is completely laughable.