Former Home Secretary Jack Straw said delays in the 'plebgate' investigation risked bringing the police into disrepute.
He told BBC Radio 4's Today programme: "We're not police officers, we're not investigators.
"What I've said in my letter to Theresa May is that whilst as the Home Secretary, as I know very well, it's not appropriate to seek to influence the outcome of an investigation, it is certainly appropriate, certainly in my experience a lot, to find out what is going on in an investigation.
"In particular why delays are taking place, which frankly have the risk of bringing the police into some level of disrepute and that is a responsibility of the Home Secretary."
More top news
Protesters angry that far-right leader Marine Le Pen is advancing the French presidential runoff are scuffling with police in Paris.
Polling projections show the far-right leader Marine Le Pen and centrist Emmanuel Macron leading in the first-round of the French election.
Winds veer northerly overnight and a band of patchy rain moves slowly southwards - wintry in places.