Online political adverts should be labelled or “imprinted” to show who is paying for them, according to the Law Commission, which warns that there is a “very real risk of the electoral process losing credibility”.

Presiding officers should also have the power to cancel polls in the event of major terror attacks as well as severe weather such as widespread flooding or other disruptive events, the commission has proposed in a series of measures to change the Victorian-era laws that govern how democracy operates in the UK.

The report, produced in the aftermath of the 2016 EU referendum and the cancelled 2014 Tower Hamlets mayoral election, will be handed to the Cabinet Office and the devolved Scottish government for approval. It was completed before the UK government announced last week the postponement of local elections and the mayoral contest in London.

The Law Commission’s review is aimed at modernising ballot rules and bringing them together in a single, consistent legislative framework. Other changes proposed include simplifying the nomination process.

Some proposed changes are in response to digital developments. In 2017, 42.8% of the total reported campaign advertising spend was online. Much of it was delivered using micro-targeting techniques, which blur the previous distinction between national and constituency electoral expenditure, the commission acknowledges.

“Without knowing who is responsible for material, it is difficult to tell when an offence has been committed, or to enforce the campaign expenditure rules,” it notes. A system requiring online adverts to carry “digital imprints” would help. “Being able to track the origin of campaign material is also important for voters, as it enables them to assess its credibility.”

Currently, printed campaign material must be labelled, or “imprinted”, with the name of whoever publishes it and with certain other information. Failure to do so is a criminal offence.

Nicholas Paines QC, the public law commissioner at the Law Commission of England and Wales, said: “Elections are fundamental to democracy yet the laws governing them are no longer fit for purpose. If left as they are, there is a very real risk of the electoral process losing credibility, which could be catastrophic.

“Our reforms will simplify, modernise and rationalise the law. This will make it easier to amend legislation so elections are able to overcome future challenges, and help to maintain confidence in the electoral system.”

Lady Paton, the chair of the Scottish Law Commission, said: “For both Scotland and the wider UK, it’s vital that the law on elections is easy to administer, accessible and user-friendly. These reforms will achieve this, ensuring elections work and are fit for the 21st century.” The report has been published jointly by the two commissions which review outdated legislation.

UK electoral law is currently spread across 25 statutes and 30 sets of regulations, many dating back to the 19th century. A significant proportion of them are found in the Representation of the People 1983 Act. When changes were last made to to allow those queuing at the close of polls to cast their vote, or example, alterations had to be made to 10 distinct pieces of legislation.

The main changes proposed include:

• Expanding the conditions under which polls can be suspended. Voting can currently only be stopped by a presiding officer in response to rioting, open violence or the death of a candidate. The Law Commission recommends allowing for any incident where a significant portion of electors are affected and unable to vote including, for example, flooding, adverse weather or an act of terrorism.

• Introducing a single set of nomination papers for candidates, replacing the existing, confusing mixture of forms and authorisations. UK parliamentary nominations at present involves up to seven different pieces of paper: some are sent by the party nominating officer, some by the candidate; some must be delivered by hand, others can be delivered by post.

• Requiring “digital imprints” for online campaign material and for social media advertisements. They would include information on who has paid for the advert, as is the case for traditional election leaflets and advertisements.

• Reforming how election results can be challenged. The new proposals would give courts the power to “weed out ill-founded claims that waste court time”.

• Simplifying the offence of bribery for anyone acting with an intention to procure or prevent the casting of a vote at an election. The ancient offence of “treating” – providing meat, drink or provisions to influence voters’ behaviour – should be abolished.

• Enabling returning officers to reject nominations that use a candidate’s name designed to confuse or mislead electors.

• Introducing sentences of up to 10 years in prison for serious electoral fraud. Prosecutors currently have to resort to the offence of conspiracy to defraud to impose such prison terms.

Minister for the Constitution and Devolution Chloe Smith said: “This Government is committed to updating electoral law and delivering a democracy that works for all in the 21st century. I am grateful for the Law Commissions’ report and will be considering their recommendations carefully.”

The cabinet office said that the government has already committed to introducing a requirement for inserting ‘imprints’ in digital election material.