 By 5 September the industrial action had spread with a quarter of the country's postal workers on strike, and by the time an agreement was reached the following week, the strike had spread throughout the British mainland (workers in Northern Ireland did not strike).No mail was being delivered by this point and, in order to ease the backlog of post, bosses at Royal Mail placed an embargo on the delivery of overseas mail.By the time the strike ended there was a backlog of 150 million undelivered letters and parcels.