Mrs Merkel previously threatened the UK with cuts in access to the EU’s single market if Britain does not want to comply with the four European Union freedoms.
But it was hoped the tough stance could be softened if Ms Merkel agreed a coalition deal with the centrist FDP after the September 24 election.
And its leader Christian Lindner has also expressed his understanding of the UK position, saying: “Europe and Germany won’t do better if the Brits are weakened — quite the opposite.
“We have an interest in a strong and economically prosperous Britain.”
But rating agency Scope warned the “uncompromising” negotiating position of the EU will not be weakened regardless of whether the FDP can secure enough seats to make up a coalition deal with Mrs Merkel’s CDU.
The watchdogs based in Berlin predicted that hopes for a “more co-operative approach” would be dashed regardless of the outcome as Germany will likely continue with its hardline stance.
Scope Manager Giacomo Barisone said: ”Although a coalition, including the FDP, is likely to have an open ear for British concerns, this difference will probably not fundamentally alter the German position towards Brexit.”
And he warned that exit talks could ultimately go well beyond the targeted two years.
Mrs Merkel is expected to win the German election with recent polls suggesting the Chancellor will win over one third of votes, putting her party on 34.2 per cent.
The SPD and rival Martin Schulz trail behind at 22.5 per cent, while anti-immigration party AfD come in at third with 12.7 per cent.
The FDP have a long history with Mrs Merkel and her CDU-CSU conservatives, meaning there is significant chance they will be part of the next government should the Chancellor fail to make a deal with rival Martin Schulz and the SPD.
And its leader Mr Lindner appears to be more flexible in his approach to Britain leaving the Brussels bloc.
He said: “All options need to be on the table [in the negotiations], including a customs union, a free-trade area, access to the single market.”
However despite the centrist party’s laid back approach, the FDP have tended to fall into line obeying Mrs Merkel’s mantra that there will be “no cherry-picking.”
Mr Lindner added: “There must be no cuts in the ‘four freedoms’ of the single market.”
(Additional reporting by Monika Pallenberg)