MTR will run the franchise with First Group for seven years from August, taking over from Stagecoach.
Strikes At Thames Valley Post Offices
Workers at hundreds of Post Offices strike in a dispute over closures, jobs and pay.
Members of the Communication Workers Union will walk out for half a day from 12.30, the eighth round of industrial action since Easter.
The union is campaigning against plans to franchise or close 75 of the Crown offices - the larger branches usually sited in high streets - saying it will hit jobs, and adding that staff have not had a pay rise for more than two years.
Post offices in Andover, Basingstoke, Bracknell, Maidenhead, Oxford, Reading, Windsor, Witney and Wokingham are affected.
CWU deputy general secretary Dave Ward said: "Post Office plans to close offices, cut jobs and reduce services cannot go on unchallenged. It's time that Government stood up for these highly-valued local services which their constituents are signing petitions for in their tens of thousands. We are calling on chief executive Paula Vennells to now lead talks to resolve this.
"Our members are taking a strong stand with this latest, eighth round of strike action. Their determination has been unwavering because they know they are right. They are standing up to protect jobs, services and for a fair pay rise.
"The company is in disarray and clearly out of touch with both its staff and customers.''
The union said the strike will affect up to 4,000 staff working in 372 Crown offices. Tens of thousands of people have signed petitions against the plans.
The Post Office has argued that the Crown offices are losing money, adding that most of the 75 will be moved to other stores under franchising arrangements.
Thames Valley Police has launched an appeal for witnesses after a fatal collision in Aylesbury.
It crashed and landed on its side near the bank of the River Thames at Mapledurham.
A vigil will be held in Oxford tonight for the victims and their families after Wednesday's attack in Westminster.
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