The Labour leader said his party is willing to support Mr Johnson’s new Brexit legislation if he addresses ‘substantial cross-party concerns’.
Sir Keir also accused the Prime Minister of having ‘turned the clock back’ and of ‘reigniting old rows’ by working to override elements of the Withdrawal Agreement which he agreed with the EU last year.
Sir Keir Starmer has said Labour will back Boris Johnson’s Brexit plans if the PM removes the parts which break international law
The PM sparked a major row with Brussels after he published the UK Internal Market Bill.
The legislation will enable the UK to unilaterally make decisions on key issues, like customs arrangements between mainland Britain and Northern Ireland, contained within the Withdrawal Agreement.
Brussels is adamant that the decisions must be made by a joint committee made up of people from both sides.
The Government has admitted its proposals will break international law, prompting fury from Mr Johnson’s political opponents but also from Tory backbenchers.
The EU has given Mr Johnson until the end of the month to withdraw the plans or face legal action, with trade talks also at risk of collapse if the PM does not perform a U-turn.
The Bill aims to prepare the UK for life outside of the EU and Sir Keir said Labour will support the legislation if the offending parts are taken out.
Writing in the Sunday Telegraph, he said: ‘We should be getting on with defeating this virus, not banging on about Europe. Get on with Brexit and defeat the virus. That should be the Government’s mantra.
‘Labour is prepared to play its part in making that happen. If the Government fixes the substantial cross-party concerns that have been raised about the Internal Market Bill, then we are prepared to back it.
‘But if it does not, and the talks collapse, then it is its failure and incompetence that will have let the British people down.’
However, the changes necessary to win Labour’s support are understood to be major, with it needing to no longer risk breaching international law and to address devolved administrations concerns of a Westminster ‘power grab’.
The Government has made clear it has no plans to change the legislation which means Labour support is unlikely.
Mr Johnson is facing pressure from all sides to change the UK Internal Market Bill which MPs are due to debate for the first time tomorrow
Sir Keir also hit out at the Government for setting out proposals which will break international law while ministers tell people they must stick to lockdown rules.
He said: ‘At a time when we are all doing everything we can do to follow social distancing rules, ministers are on the television and radio justifying why it is OK for them to break international law. It is as ludicrous as it is frustrating.’
The UK Internal Market Bill is due to be debated for the first time in the House of Commons tomorrow afternoon.