Tens of thousands protested Saturday under sunny skies in London against plans for Britain to withdraw from the European Union.

:: German government officials have proposed giving Britain access to the European Union’s single market in return for a fee, Focus magazine said on Saturday citing a Finance Ministry report.

The 35-page report on the potential costs of Brexit to Germany said Britain’s departure from the EU risked “serious economic and stability relevant consequences; effects in particular on the real economy.”

The ministry officials calculated Berlin would have to pay an additional 4.5 billion euros ($5 billion) a year into EU coffers as a result of Britain’s departure from the bloc.

To mitigate the cost, they floated the idea of charging Britain for access to the single market.

“Such a future financial contribution should be used to alleviate the financial consequences of Brexit (reduction in EU spending or increase in payments for other member states),” Focus quoted the officials as saying.

A Finance Ministry spokesman declined to comment on the Focus report when contacted by Reuters.

Brexit would also put additional strain on German tax and customs officials as there would be new tax liabilities for products and services bought from British companies, the report said.