A police officer has spoken of his anger after receiving a 'thank you' card from Lord Janner after an investigation into child sex abuse claims against the peer was dropped.

Labour politician Janner wrote to Kelvyn Ashby – then a detective inspector at Leicestershire Police – after police chiefs decided not to arrest him over serious allegations in the early 1990s.

Ashby was left fuming by the decision and says his team had found evidence against Janner. He spoke of his "disgust" after the Lord invited him and his wife to join him for lunch in a Westminster Christmas card.

Recalling the episode, Ashby told the Mail: "The card was an official House of Commons Christmas card and was handwritten.

"It said something like 'I was very pleased with the way you treated me' and invited me and my wife for a dinner at the House of Commons. I couldn't believe it. My wife was disgusted, as was I. Needless to say we never replied and never went."

Janner has been at the centre of historical allegations that he sexually abused youngsters during his earlier political career by exploiting his position. The Crown Prosecution Service has admitted it should have prosecuted him three times over the claims.

Janner's family have issued a statement saying that he is "entirely innocent of any wrongdoing".

News this month that Janner shall not be sent to trial due to his ailing health from Alzheimer's was met with an outcry.

According to Ashby, there was pressure from his superiors to back away from the Janner case, due to the peer's position in British society. He called the experience "frustrating".

"Someone higher up told us that we couldn't just arrest an MP and it went no further," he said.

"We were told that by someone senior, who I can't name, but the order had to have come from the very top. I'm sure my bosses' hands were tied. I was extremely frustrated. Janner should have been arrested. He was treated differently because he was an MP."