An “embarrassing” tranche of messages set to be released in the next fortnight will expose the “cosy relationship” between Government ministers and disgraced peer Lord Peter Mandelson, The i Paper can reveal.

These documents will be included in a second wave of files relating to Lord Mandelson’s appointment as US ambassador, which are expected to be published after MPs return to Parliament on 1 June.

Sources familiar with the contents told The i Paper that the documents include “embarrassing” messages showing that some ministers were “sucking up” to the peer.

While the revelation is likely to heap more pressure on Sir Keir Starmer as he fights for his political survival, insiders claim there is no “smoking gun” likely to bring down the Government.

The source added: “The messages are more embarrassing than anything else and reveal a far too cosy relationship between some ministers and Lord Mandelson.”