A former minister has launched a scathing attack on Sussex police which spent six months investigating him for alleged racist abuse after describing a "nightmare constituent" as "unkempt".

Tim Loughton said Kieran Francis had serially abused him and his staff, including calling the MP a "f****** Nazi" and an "arrogant, racist lying a*******".

But when Mr Loughton responded in an email describing his constituent as unkempt and talking "self-serving b******s" Sussex Police began an investigation which involved the MP being interviewed under caution.

Former children's minister Mr Loughton, MP for East Worthing and Shoreham, said he will make a formal complaint against the force and also criticised Chief Constable Martin Richards' handling of his grievance.

Speaking in the Commons, Mr Loughton described how Mr Francis, from Shoreham, was a "serial complainer with more chips on his shoulder than McCain" but "when he doesn't get his way he becomes abusive".

Mr Francis complained to the MP after he was described in an internal Adur District Council document as "unkempt".

Mr Loughton said: "I investigated and then sent an email back to my constituent saying that, given the dictionary definition of unkempt is 'untrimmed, dishevelled and rough' the council's description - not mine - struck me as eminently accurate. Anyone who has seen a photograph of the pony-tailed, shaggily bearded Mr Francis could not but concur.

"For good measure, and uniquely in almost 16 years of being a constituency MP but probably unwisely, I let my true feelings get the better of me and referred to Mr Francis' latest whinges as 'self-serving nonsense' except the word I used in place of nonsense, the word I took off Mr Francis' own blog ... was b******s."

Racism complaint

The email led to a police complaint from Mr Francis, who claimed he was a Romany Gypsy and the term unkempt was racist.

The MP was interviewed under caution for 90 minutes on suspicion of sending a malicious communication, and it was more than six months before he was eventually informed that he was in the clear in February.

Mr Loughton criticised the response of the Chief Constable in a meeting last week. "I was treated by the Chief Constable Martin Richards as if I was not only the subject of ongoing criminal investigations but almost as if I had been charged and found guilty," he said.

Responding to the debate, Deputy Commons Leader Tom Brake said he had "no responsibility for the police and will not attempt to answer for the conduct of Sussex Police".

But he added: "I'm sure every MP present in the House will have sympathy with his remarks about the amount of time and resources devoted to this investigation given the nature of the allegations."