The Metropolitan Police confirmed they had acted on a "complaint" from the Society of Black Lawyers after the European champions accused referee Clattenburg of using comments understood to have been interpreted as racist in the club's acrimonious Barclays Premier League defeat to Manchester United on Sunday.
Press Association Sport understands the 37-year-old completely denies the allegations against him, which are also the subject of a Football Association investigation. Clattenburg and his fellow professionals were said to be shocked and angered by the claims as the refereeing fraternity rallied around their colleague.
There were also suggestions of seething resentment in some quarters at the way Chelsea had made their complaint against Clattenburg public and a desire to see strong action taken against them if the official was cleared. That could take weeks or even months after the police became involved in proceedings less than 24 hours after the FA's investigation began.
Chelsea themselves could yet make a criminal complaint, having appointed an external legal team to conduct their own probe, something which is expected to conclude on Wednesday. And the FA may be forced to postpone their inquiry if the police request they do so, something they came under heavy fire for during the year-long John Terry scandal.
It is the second time in 12 months the Metropolitan Police have become embroiled in a high-profile football racism case after the man behind the mooted black players' breakaway union, Peter Herbert, wrote to them demanding they investigate Clattenburg. Herbert defended his intervention on Tuesday afternoon, telling Sky Sports News: "What we don't want is for it to be swept away under the carpet. It must be subject to a full and proper investigation."
But Professional Footballers' Association chief executive Gordon Taylor said: "Involving police or waiting causes a massive festering of the issue, which has continued to cause problems and is not good for the image of the game. Football has got to be confident enough to deal with it. I have said that to the House of Commons, the FA Council."
Clattenburg, who vowed on Sunday to co-operate fully with any investigation, was expected to be spoken to by both police and the FA, possibly after submitting a written account about what took place during Sunday's game. He has already filed what is known as an 'extraordinary incident report', which is understood mainly to deal with an alleged confrontation that took place in the referees' room after full-time.
Sources have told Press Association Sport Chelsea manager Roberto Di Matteo, assistant manager Eddie Newton and chief executive Ron Gourlay were all present as Mikel angrily accused Clattenburg of having abused him during the match itself. The referee, his assistants and fourth official are understood to have been stunned by the claims, with Michael McDonough, Simon Long and Michael Jones - who were miked up to Clattenburg - denying hearing anything of that nature.
It is unclear whether Clattenburg will elect to continue refereeing or take a break from the game while any investigation was pending but he has accepted being stood down from officiating in the coming week.
Source: PA
Source: PA