This would mean free movement of migrant labour from other EU countries effectively remains in place, despite claims from the Leave camp that immigration could now be brought under control of Westminster.
Prominent Leave campaigner and Conservative MEP Daniel Hannan is among those who have already backed such an approach to withdrawal negotiations from the EU.
Mr Hammond said yesterday: “We will not be able to negotiate control of migration from the EU and at the same time have full access to the single market. There will have to a trade-off.”
Mr Hammond, who backed Remain, insisted the UK will resist pressure from Brussels and other EU capitals for a swift start to negotiations on its withdrawal from the bloc.
Despite a demand from European Commission president Jean-Claude Juncker – backed by the foreign ministers of France and Germany – for the process to begin “immediately”, Mr Hammond insisted that “nothing is going to happen at the moment”.
The timing of the formal notification of intention to leave the EU, set out in Article 50 of the Lisbon Treaty, is in Britain’s hands and talks will not start until a new prime minister is chosen to replace David Cameron, he said.
His comments came as Washington confirmed that Secretary of State John Kerry will come to London today for talks with Mr Hammond as the US grapples with the fallout from Thursday’s referendum.
Mr Kerry will also travel to Brussels, where he is expected to emphasise US backing for the European project amid speculation that other member countries could follow Britain’s lead.
But while he is likely to echo Barack Obama’s assurances of a continued “special relationship” between the UK and US, it is unclear whether he will have advice for London on how to respond to voters’ shock demand for withdrawal from a union which Washington regards as key to stability in Europe and a crucial partner in wider geo-political arenas.
Invocation of Article 50 sets in train a two-year process of thrashing out a new relationship between the UK and its former EU partners.
Leading Leave campaigners, including Boris Johnson have indicated that they do not want the government to be rushed into taking this step.
Mr Hammond told ITV1’s Peston on Sunday: “The Prime Minister is clear that the correct way to do this is for the new prime minister to make the decision. There is no imperative upon us to serve the notice at any particular time. The referendum is an internal matter, the British Government as a member of the European Union is entitled to serve that notice, but the timing is entirely one for the UK to determine.”
Mr Hammond made clear that he wanted the future PM to make continued access to the European single market the primary objective of withdrawal negotiations, in a “trade-off” which must mean accepting limits on the UK’s ability to control immigration from the remaining 27 states.
It was “essential” to maintain single market access in order to continue to attract foreign investment without which Britain cannot “pay our way in the world”, he said, warning: “Loss of that access now would be catastrophic.”
Foreign direct investment into the UK has already “all but dried up” as companies wait to see the consequences of the Brexit vote, the foreign secretary said.
Mr Hammond said that he and other Cabinet members – including Chancellor George Osborne – would remain in office until the selection of a new Conservative leader, expected by the time of the party’s annual conference in October.
Tory grandee and ardent europhile Lord Heseltine has called for Boris Johnson, Michael Gove and Nigel Farage to be in charge of Brexit negotiations.
The former deputy prime minister said he was “appalled” by the result of the referendum as he said voters had been “sold a fool’s promise”.
While he said the decision to leave must be respected, the Tory heavyweight stressed the need for Brexit leaders to be held accountable for the promises they made in the run up to 23 June.
He said: “It is essential that the negotiations are conducted by Boris Johnson, Michael Gove and Nigel Farage, the architects of this policy.
“Any other negotiating team will produce claims that those three would have achieved a better result and during the negotiations they will excuse any deterioration in Britain’s position as a failure of the negotiators.
“They must be in charge and must be seen to be in charge.”