Four more people, including two serving police officers, have been arrested as part of an investigation into suspected fraud and bribery at the Police Federation of England and Wales.

Two men and two women were arrested at the federation's offices in Leatherhead, Surrey, on Tuesday. The women are both in their 50s and the men in their 40s and 50s.

The City of London Police's corruption unit, which leads on fraud investigations, said all four suspects had been taken to a police station for questioning. It comes after three arrests connected to the same case were made in March.

The Police Federation represents more than 145,000 rank-and-file officers, up to and including the rank of chief inspector as well as special constables.

Det Supt Jim Halkett said the investigation "continues to make significant progress, with officers working through a number of lines of inquiry to establish the full facts and circumstances surrounding this case".

Police said the four people arrested on Tuesday were being questioned on suspicion of fraud by abuse of position of trust. One of the women and the man in his 50s were also being held on suspicion of bribery and fraud by failing to disclose.

It comes after the three men were arrested in March on suspicion of fraud by abuse of position - a 51-year-old from Wales, a 55-year-old from Bristol and a 46-year-old from Surrey.

Police said the three either currently or previously "occupied senior roles within [the Police Federation's] governance and operational structure".

Police Federation chief executive Mukund Krishna is understood to be among the three. The federation confirmed he was suspended from his role "due to an ongoing police investigation" in a statement issued days after the arrests.