PEERS have warned that Holyrood’s desire to lower the voting age for Scottish elections when it gets more devolved powers could “cause problems” by MSPs having to give the vote to some imprisoned criminals too.

The claim by the House of Lords Constitution Committee in a report on the Scotland Bill echoes that of the Upper House’s Economic Affairs Committee.

It complained last week that without publication of the full details on how the so-called fiscal framework on the new powers would work, then parliamentarians were being asked to debate the legislation “in the dark”. Peers have called for the legislation to be halted until the framework can be fully assessed.

Ahead of today’s first main debate on the Scotland Bill by peers, the constitution committee issued the document, which referred to how the legislation could “cause problems regarding prisoner voting rights as – unlike the UK Parliament – the Scottish Parliament cannot make laws that are incompatible with convention rights under the European Convention on Human Rights(ECHR)”.

It went on: “The UK’s blanket ban on prisoners voting has been deemed incompatible, meaning that unless some prisoners were to be enfranchised in Scotland, legislation on the franchise there might be invalid.”

The Committee insisted that the UK Government had failed to address the issue and nor did the bill, “meaning the potential problem still remains”.

It added that in today’s and in subsequent debates, the Lords might seek “clarification from the Government as to how they will ensure the Scottish Parliament will be able to exercise its powers over the franchise in a way compatible with convention rights”.

The issue of prisoners’ voting rights is a deeply contentious one. David Cameron famously said that the idea of imprisoned criminals having the vote made him “physically sick”.

In July 2014, the UK Supreme Court dismissed a bid to overturn the ban on convicted prisoners being able to vote in the Scottish independence referendum.

Two killers, serving life sentences, had launched an appeal having already had their case rejected by judges at the Court of Session in Edinburgh. They claimed the voting ban infringed their human rights.

At the time, the Scottish Government welcomed the ruling, saying it confirmed the approach taken; that the 2013 Scottish Independence Referendum Act was “compatible with the ECHR and European Union law and that convicted prisoners currently serving a custodial sentence will not be able to vote in the referendum".

Earlier this year, Kenny Macaskill, the former Scottish Justice Secretary, admitted he had been “complicit” in the Scottish Government’s opposition to prisoner voting, saying it was the wrong thing to do albeit for the right reasons ie avoiding lurid headlines in the run-up to the referendum.

"To have credibility on the issue the Scottish Government must now review their position on votes for prisoners or the defence of the Human Rights Act will ring hollow," he argued.

Last month, the Prime Minister insisted prisoners would not get the vote after the European Court of Justice ruled that the vote could be stripped from inmates who had been convicted of “serious” crimes.

But legal experts suggested the ruling cast doubt over Britain’s blanket ban, noting that criminals serving short sentences could launch court action to win the vote.

Mr Cameron said at the time: “I'm very clear, prisoners shouldn't get the vote and it is matter for the British Parliament. The British Parliament has spoken. The Supreme Court in Britain has spoken, so I’m content to leave it there.”

But last night Patrick Harvie, leader of the Scottish Greens, said: “The blanket ban on prisoner voting is already a breach of ECHR as well as being irrational.

“Votes at 16 was clearly a successful and well-received aspect of the independence referendum. We should not allow barriers to be placed in the way of following through with the same policy for all elections,” added the MSP.