Allegations that four members of the Welsh assembly have failed to fully declare interests have been referred to the police.

An investigation by BBC Wales programme Dragon's Eye led to concerns that Labour's Ann Jones, Conservative Mark Isherwood, Eleanor Burnham from the Liberal Democrats and Jocelyn Davies of Plaid Cymru had all paid their spouses from assembly funds but had failed to register their work.

"A protocol exists between South Wales Police, the Crown Prosecution Service and the National Assembly for Wales with regards to such allegations," said chief superintendent Jeff Cooksley.

"In accordance with this protocol, the matter has been reported to South Wales Police."

A spokeswoman for presiding officer Dafydd Elis Thomas added that details of the spouses' employment had only been registered last week.

Failing to declare the occupation of their partners could result in a fine of up to £5,000.

"If someone has failed to register an interest, whatever that interest is, then it's potentially a criminal matter," said Kirsty Williams, Liberal Democrat AM and chairman of the assembly's standards committee.

"Any complaint that was received here at the national assembly by the presiding officer would immediately be sent to the police for investigation."

Three of the assembly members were unavailable for comment, but Mark Isherwood, a North Wales assembly member, defended himself against the allegations, claiming he was unaware he was breaking the rules.

"I pay my wife for five hours a week which works out to be about £100 a month," he said.

"As soon as I realised the breach I contacted the presiding officer immediately to remedy the situation.

"I have always been completely honest about the fact she does some work for me."