Organisations in charge of preparing the county when Britain leaves the EU fear hauliers turning up to Portsmouth port without the right paperwork could cause gridlock.
Mitigation measures are being put into place as the country races toward the October 31 deadline with uncertainty over MPs agreeing Boris Johnson’s Withdrawal Agreement.
It comes as planners fear up to 70 per cent of lorry drivers will arrive at the port heading to the EU without the right papers. A tailback of just 13 lorries will see queues on the M275 leading to the motorway being shut.
So far the government has given £1.25m to Hampshire County Council and Portsmouth City Council for construction works for the mitigation plans.
Today the Hampshire Local Resilience Forum said:
:: Southbound traffic on the M275 will be cut to 40mph from 60mph from Friday (October 25).
:: A series of checkpoints on the A31 and Tipner West will cost £80,000 a week operational.
:: Around 130 people will be trained to check hauliers have the correct paperwork.
:: The Tipner lorry park previously set to stack 40 lorries as a holding area will instead be used as lanes to check four lorries at a time.
:: A 230-lorry capacity stack will be used at the A31 with a 200-lorry overflow on the A303 if needed.
HGVs will be checked at the A31 and given a permit to go to the port, or sent off. Tipner West will be used to check paperwork as well.
Around 600 lorries arrive at the port each day, with 48 sailings a week - 31 to France, eight to Spain and nine to the Channel Islands.
The contingency plans will only kick in if there is a prospect of a no-deal Brexit.
Hampshire chief fire officer Neil Odin, chair of the strategic co-ordinating group for the LRF, said: ‘As a team of organisations across Hampshire and the Isle of Wight we’re planning for what is the reasonable worst case for EU exit.
‘If we leave without a deal the port of Portsmouth may become blocked by lorries that aren’t prepared for the border.
‘The reasonable worst case is that up to 70 per cent of those lorries may not be ready so we’re putting in plans to make sure they’re ready, including pop-ups up-stream in places like Rownhams and services like that.
‘But also holding areas and checking facilities to make sure lorries are ready for the crossing without undue traffic disruption to Portsmouth and the surrounding areas.
‘(The work is) to try and keep Portsmouth flowing, keep the port operating, keep the freight going in and out of the UK and to keep the population of Portsmouth to move around their daily lives.
‘We’re doing that by triaging lorries so that they’re ready for the border and they can go about their business in the normal way.’
On Saturday MPs in the House of Commons backed the Letwin amendment, meaning approval for Mr Johnson’s deal is held until the Withdrawal Agreement Bill is passed in the House of Commons.
Portsmouth South MP Stephen Morgan backed the amendment, which could lead to a delayed EU exit. Conservatives Portsmouth North MP Penny Mordaunt, Gosport MP Caroline Dinenage, Havant MP Alan Mak, and Fareham MP Suella Braverman all voted against the delay.