By Jonathan Davies

The UK Serious Fraud Office (SFO) says it is actively assessing "material in its possession" relating to allegations of corruption in FIFA.

The SFO said it "has made plain that it stands ready to assist ongoing international criminal investigations".

Elsewhere, UK Prime Minister David Cameron called for FIFA president Sepp Blatter to resign and said the "sooner the better".

Speaking in Berlin, Mr Cameron said: "You cannot have accusations of corruption at this level and on this scale in this organisation and pretend that the person currently leading it is the right person to take it forward.

"That cannot be the case. Frankly, what we've seen is the ugly side of the beautiful game and he should go.

"And the sooner that happens the better - the faster that organisation can start to rebuild its credibility, which is going to be so important because so many people around the world want to see this game properly managed, properly looked after, so we can all enjoy the World Cups of the future."

Several FIFA officials were arrested in Zurich on Wednesday after the US Department of Justice indicted nine FIFA officials and five corporate executives.

Separately, Swiss authorities launched an investigation into alleged corruption in the awarding of the 2018 and 2022 World Cups in Russia and Qatar.

In November, the SFO called for anyone with information to come forward relating to alleged corruption in the bidding process for the World Cups.

The allegations came as FIFA comes together for its Congress where president Sepp Blatter is seeking re-election for a fifth term.

A number of FIFA vice-presidents and members of its executive committee face allegations of corruption, prompting widespread condemnation of Mr Blatter.

FIFA sponsors have raised concerns over the allegations and UEFA, the European football governing body, has even suggested that its nations could boycott the 2018 World Cup if Blatter is re-elected.

UEFA president Michel Platini says he twice asked Mr Blatter, to his face, to resign. But on both occasions his request was rejected.