Germans were speculating over the “beginning of the end of the Merkel era” on Tuesday night after the chancellor suffered a shock defeat in a key vote of her party’s MPs.

For the first time since Angela Merkel took power almost 13 years ago, MPs from her Christian Democrat party (CDU) rejected her chosen candidate as their leader in parliament and voted instead for a challenger who had promised to be more independent.

The defeat was a body blow to Mrs Merkel’s authority and left her facing the prospect of backbench rebellion as she tries to get her coalition’s legislative programme through parliament.

“This is an uprising against Merkel,” Thomas Oppermann, a senior MP from her coalition partner,...