The latest walkout affects the OX1 and OX2 postcode areas

The wildcat industrial action, which began at the main sorting office in Cowley over claims of bullying, is now in its 11th day.

The situation remains unresolved despite talks between Communication Workers' Union members and Royal Mail.

Both sides hope to make progress when they meet for talks on 14 April.

Counselling service

Earlier this week, delivery staff from Headington and central Oxford delivery office also walked out in support of their colleagues.

On Wednesday, Royal Mail announced it had set up "an independent counselling service for employees following allegations of harassment at Oxford Mail Centre".

In a statement the company said: "The move is a demonstration of Royal Mail's commitment to eradicate bullying and unacceptable behaviour in our workplace.

"The establishment of this service is in addition to the measures already taken to resolve the unofficial industrial action, which began on Tuesday 30 March."

The confidential service, available from next Wednesday, will be operated by an external organisation and will enable all employees to have face-to-face advice and raise any concerns they may have.

An independent inquiry into "cultures and behaviours" at the Cowley mail centre is expected to begin when staff return to work.