HMP Glasgow, the new £1bn prison being built to replace Barlinnie, will be too small to solve an overcrowding crisis, Scottish Labour leader Anas Sarwar has warned.

The capacity expected to be added to the Scottish prison estate with the construction of two facilities will not be enough to house the current population.

The current design capacity of the estate is 7,805 inmates, but as of last Friday, the total population was 8,391. Scotland’s prisons have been struggling with overcrowding for years, with a new record high reached last month. Analysis by Scottish Labour has shown that if the new facilities increase capacity as intended, they will still not be able to house the current population.

HMP Glasgow – which could cost as much as £1 billion and will replace the current Victorian-era HMP Barlinnie – will increase capacity by 357, while HMP Highland will allow the estate to house 107 more inmates. When added to the current capacity, the figure rises to 8,269 – more than 100 places under the current requirement.

In February, it was confirmed that the replacement for Barlinnie prison will cost nearly £1bn, almost double the previous estimate. Justice Secretary Angela Constance stated a cost of £998.4m for HMP Glasgow in a letter to the criminal justice committee. The current timeline is for the prison to open in 2028, three years later than originally planned.

Constance said the "significant increase" in costs, from a previous estimate in 2022 of £400m, was due to wider increases across the construction sector.

Scottish Labour leader Anas Sarwar said: “The SNP are ploughing ahead with their plans to spend over £1 billion on HMP Glasgow – the same as it cost to construct the five-star Atlantis Hotel in Dubai, one of the most luxurious hotels in the world,” he said.

“Yet these alarming figures show that despite the eye-watering cost of this new facility, it will not even be fit for purpose by the time it has been completed, with Scotland’s prison population already at a record high. That means taxpayers will be paying well over the odds for a prison that was supposed to cost £100 million, and which will not even fix the crisis in our prisons estate, with staff warning that they are at a crisis point.

“This is a mess of the SNP’s own making. Scots are having to foot the bill for SNP incompetence, with ministers out of ideas for getting on top of this dire situation.”

A Scottish Government spokesperson said: “Replacing HMP Barlinnie is essential for long-term sustainability of the prison estate in Scotland.

“HMP Glasgow will add 357 places to the overall estate, transform how prisoners are rehabilitated, improve staff working conditions and generate up to £450 million worth of economic benefits, including jobs and contracts for businesses in Scotland.

“HMP Highland will provide an additional 107 places and will allow more adult men from the Highlands and Islands to be accommodated in their local area, improving access for families and services.

“We recognise the serious challenges facing the prison system, which is why the Justice Secretary announced in Parliament emergency proposals to tackle prison overcrowding, with stringent safeguards to protect public safety.

“Our paramount concern is to ensure that those who work and live in prisons are kept safe, so immediate action is now necessary.”

A Scottish Prison Service spokesperson said: “HMP Glasgow will deliver fit-for-purpose, safe and secure accommodation, and have a transformative impact in how we support and rehabilitate people.

“However, we are managing an extremely high and complex population which is having an increasingly destabilising impact on establishments across Scotland, and this requires action to be taken now.

“We need to see a reduction in our population so our staff can fully support people in our care, reduce their risk of reoffending, and help build the safer communities we all want to see.”