The wildcat industrial action by workers from Oxford's main Royal Mail sorting office began on Tuesday night.

The dispute is over a number of claims of bullying at the Cowley office.

Talks between unions and Royal Mail bosses continued on Saturday. Union representatives say they will now put a list of proposals to workers on Monday.

Hundreds of thousands of letters have been caught in the backlog since the strike began.

We want to investigate these allegations but it's not helped when three-quarters of your staff are out in the car park Richard Hall, Royal Mail

Workers claim they are not being taken seriously enough but Royal Mail says an internal inquiry is under way.

On Friday, Royal Mail spokesman Richard Hall highlighted the firm's investigations.

He said an independent inquiry team, backed by an external company, was being brought in to look at "behavioural attitudes across all the shifts".

Mr Hall told BBC News Online: "We feel that this is the right way of going about this.

"We want to investigate these allegations but it's not helped when three-quarters of your staff are out in the car park.

"The message to staff is to return to work."

The Communications Workers' Union (CWU) has claimed that about 90% of the workforce has taken part in the unofficial strike action.

The centre was also hit by a series of wildcat strikes last year.