"I would like to see a very stringent review by UEFA because I know they take racism very seriously," he told ITV Sport.

"If we say 'we've got zero tolerance for racism', one person making monkey chanting noises is the same as 100 – zero tolerance is zero tolerance.

"At UEFA we need to address that, but to be perfectly frank we also need to address racism in England. We still have it, we have it throughout the pyramid. We shouldn't take the moral high ground, we should join a movement to drive racism out of our game and have zero tolerance.

"UEFA are going to have to think very carefully about the level of abuse they're prepared to let players tolerate and they're going to have to decide who they are going to make an example of one day, but that's after a thorough examination of the facts."

The abuse was reported to Croatian referee Ivan Bebek who called for step one of the UEFA anti-racism protocol – a stadium announcement calling for the abuse to stop – to be enacted in the 28th minute.

However, it continued and there was a second delay close to half-time, when it appeared a group of supporters in the home section left the stadium. It is understood that this delay did not constitute the second step of the protocol – taking the players off the pitch temporarily.

The third and final step of the protocol is for the referee to abandon the game.

Clarke praised the role England manager Gareth Southgate played in the evening and said that the FA now had trained security staff taking witness statements.

It is understood UEFA will await the reports of the referee and other observers inside the stadium before making any decisions on any sanctions that should follow from the night.

Anti-racism group Kick It Out insists severe punishments must be handed out and said it was "unacceptable" that the last two steps of the protocol were not carried out.

"We are sickened by the disgusting racist abuse directed at England men's team tonight by Bulgaria supporters – including TV footage which appeared to show Nazi salutes and monkey noises," its statement read.

"We applaud Gareth Southgate, his staff and players for the actions taken in reporting the abhorrent abuse, and offer our full support to the entire squad, their families and anyone affected by those appalling scenes.

"We are encouraged that the protocol was initially enforced by the match officials, but UEFA must explain why players weren't sent to the dressing room during Step Two, as is clearly stated in the rules.

"TV footage also clearly shows that racist abuse continued in the second half, so it is unacceptable that Step Three was not enforced. This match should have been abandoned by the officials.

"It's now time for UEFA to step up and show some leadership. For far too long, they have consistently failed to take effective action. The fact Bulgaria are already hosting this game with a partial stadium closure for racist abuse shows that UEFA's sanctions are not fit for purpose.

"There can be no more pitiful fines or short stadium bans. If UEFA care at all about tackling discrimination – and if the Equal Game campaign means anything – then points deductions and tournament expulsion must follow."

ITV pundit Ian Wright welcomed the collective action taken under the protocol, calling it "a great day" in the fight against racism.

He said: "It's a terrible day for the Bulgarian people and how they have been represented, (but) it's a great day in respect of trying to tackle racism.

"We can see over in that stand with those (anti-racism) banners, they mean nothing. What we're seeing is a set of fans who do not care and need educating.

"As a black player, we've heard it for many years about walking off (in the event of racist abuse).

"But you do need your white players to do that for you, so you can go off together. When that can happen, when you can see how powerful that is, that will do something."

The president of the Bulgarian Football Union, Borislav Mihaylov, had been critical of comments made by England in the build-up, suggesting talk of the potential for racist abuse was "unjust branding" of Bulgaria and its supporters.