Sir Paul Lever said Germany’s own interests will be at the forefront of negations after the Chancellor said Britain could face consequences if the Government puts an end to free movement after Brexit.
The retired ambassador said maintaining unity in Europe and the “integrity” of the single market would be their main interest.
He told Sky News: “They won’t be a particularly sympathetic friend, they will treat us as Angela Merkel has said, fairly, objectively, pragmatically, but they have their own interests.
“And as with all German behaviour in the EU, it’s those interests which will principally motivate them.”
When asked if it was about “keeping the show on the road”, he said: “Yes, I would say their main interest in the Brexit negotiations will be to preserve the unity of the 27, to maintain the integrity of the single market, including all four of its freedoms.
“And to avoid having to pick up any of the bill themselves after we’re gone.”
Sir Paul said Britain could come up against “a hard circle to square”.
He said: “The problem with our leaving is that the people who pay don’t want to pay any more and the people who receive don’t want to get any less and that’s a hard circle to square.”
The comments come after Mrs Merkel warned against Theresa May’s vow to cut immigration, saying Britain would pay the “price” by taking control of its borders.
She also insisted the EU would consider the views of Remain voters when Brexit negotiations finally get underway later this year.
The German leader said: “If the British Government ends the free movement of people, that will have its price.
“This isn’t malicious, but they cannot say there will be an upper limit of 100,000 or 200,000 EU citizens, no more.
“That will not work. We would have to think about what obstacle we create from the European side to compensate for that.”