The post office in Streatham High Road will shut over the next year with services moved to the nearby WH Smith.

The decision sparked outrage from users and politicians, who say the change will result in a drop in standards of service for customers.

Streatham's post office is one of 70 in England, Scotland and Wales to have its services taken over by branches of WH Smith.

Alan Cook, managing director of the Post Office, said the combination of the company and WH Smith would make "perfect sense" for customers, because of links between their products.

But Streatham MP Keith Hill criticised the decision, saying: "There's only one test and that's service to post office users.

"I'm throwing down the gauntlet to the Post Office to prove this move means a better service to customers. Until they can prove that to me, I'm against this move."

Ian Ward, executive member of the Communication Workers Union (CWU), said WH Smith was merging with the Post Office to make a profit, hoping to gain business from customers using the stores for postal services.

"The company is getting a brand name like the Post Office behind it to enhance its profits at the expense of public service," he said.

"The Streatham WH Smith is not a big store - how will it fit in enough staff, counters, a queuing system and space for people to fill in forms?"

The transfer is due to take place by the end of summer 2008. Existing post office staff will be deployed to other branches or given voluntary redundancy.