MSPs will have to work longer hours and spend more days at the Scottish Parliament because of the unprecedented workload caused by Brexit, the Herald understands.

The Great Repeal Bill and related Westminster legislation needed to make withdrawal from the EU a reality are expected to have a huge knock-on effect for Holyrood.

It is understood Holyrood’s authorities are now working on how to address “capacity” issues which will arise after the Brexit legislation starts its passage through Westminster.

Possibilities include MSPs sitting on Mondays and Fridays and longer into the night.

Most of the extra work is likely to fall on Holyrood's committees as they pick through hundreds of pieces of minor legislation which will need to be reviewed in light of Brexit.

Areas most affected include agriculture, fishing, public procurement and the environment.

MSPs normally work at parliament from Tuesday morning to Thursday evening, and spend Monday and Friday on constituency business.

However there is slack in the system if required: parliament's full working week technically runs from 2.30pm on a Monday to 12.30pm on Friday, and sittings can also be readily extended into the night.

There had been speculation that Holyrood might need to sit to midnight to handle the fall-out from Brexit, but the Herald understands there is no such plan.

However Holyrood officials are liaising with the UK Cabinet Office about future workload.

Alex Salmond yesterday said Holyrood’s committees were already struggling with workload, and there should be a “relatively modest” increase in MSP numbers to address it.

Giving evidence to the Commission on Parliamentary Reform, which is looking at how Holyrood operates, the former First Minister also said the 56 list MSPs should come from a single national list, rather than eight regional ones, effectively creating two classes of MSP.

He said: "I think the list should be national as opposed to geographical. I have never been convinced by the regional aspect of the list."

He also said the prospect of either independence or further devolution of powers to Holyrood could also make the case for an increase in MSPs above the current 129.

Brexit will render thousands of obscure statutory instruments confused or meaningless as they refer to EU laws, regulations and institutions that will no longer apply to the UK.

For instance, the Waste Management Licensing (Scotland) Regulations of 2011 depend on a definition of “waste” contained in the EU Waste Directive of 2008.

The UK Government is expected to publish a White Paper outlining the Great Repeal Bill on Thursday, the day after Theresa May triggers the Article 50 withdrawal process.

The Bill and several sister bills are expected to be tabled later this year.

The Great Repeal Bill will scrap the European Communities Act (ECA) of 1972 which took the UK into the EU the following year.

Ordinarily, repeal changes the law to make it as if the original Act never existed.

However the ECA was the foundation for thousands of pieces of subsequent legislation, most of which the UK government intends to keep to avoid gaps appearing in the law.

The Repeal Bill will therefore embed, or transpose, most of these into UK law upon Brexit.

Outside the EU, the UK Government will then be free to discard any legislation it doesn’t like.

UK ministers are expected to give themselves sweeping “Henry VIII powers”, which would let them change primary legislation without parliament’s involvement, to speed up the process.

There is speculation Scottish ministers may get similar powers.

Because the Repeal Bill will affect devolved powers, Scottish Secretary David Mundell has said he expects the Scottish Parliament will be asked to give its consent to Westminster legislating on its behalf, through a legislative consent, or Sewel, motion.