Mobile phone footage allegedly shows the backlog
A backlog of 15 million letters in London following postal strikes may never be delivered, the Communications Workers Union (CWU) has warned.
The union said Royal Mail was storing the backlog in two locations in Dartford and Peterborough where casual workers were employed to sort them.
But Royal Mail told BBC London it would not "reward" strike action by paying overtime to staff who went on strike.
Of 10 test letters posted by BBC London two weeks ago, just six have arrived.
A spokesman for the CWU said: "Because of the strike there is a backlog of millions.
"Royal Mail have employed casuals - who we believe have not been security cleared - to undermine the strike and exclusively deal with the backlog."
The union said it believed they were agency workers being paid the minimum wage of £5.80 per hour.
Its spokesman added: "Royal Mail may claim these casuals are to deal with Christmas - but you do not have Christmas casuals in September."
Emily Thornberry, MP for Islington South and Finsbury visited the sorting office at Mount Pleasant - but was not let in.
She said: "It makes me think the horror stories I have been told may be true.
"If Royal Mail are not going to pay overtime I don't know when we are going to get our post."
London... via Preston
To get an idea of the scale of delays, two weeks ago BBC London posted 10 letters to the same address from across the city.
Four of the letters are yet to arrive - and the postmark on one showed it had come via Preston.
Paul Tolhurst, Royal Mail's operations director, said: "There are delays and we are sorry about that.
"But our customers would be truly surprised if, in reward for causing delays, our response was to say 'all you people who have done that, let's give you extra money through overtime'.
"We are trying to keep mail moving through other means."
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