Press release: PM call with the Chancellor Merkel: 4 March 2018

A Downing Street spokesperson said:

The Prime Minister spoke to Chancellor Merkel today to congratulate her following the vote of the Social Democratic Party membership in favour of a grand coalition. Both leaders looked forward to the formation of a new German government and to continuing to work closely together.

Link: Press release: PM call with the Chancellor Merkel: 4 March 2018
Source: Gov Press Releases