Postal workers today began clearing a huge backlog of mail as the latest wave of strikes ended, with further disruption planned in the bitter row over jobs, pay and modernisation.

Two 24-hour walkouts led to 30 million letters being delayed, around 40 per cent of an average daily postbag.

The huge backlog is set to grow next week because of another three days of strikes planned by the Communication Workers Union from Thursday.

The union said up to 120,000 workers “solidly supported” this week’s strikes, attracting support from members of the public and other workers.

Meanwhile, the GMB set up a phone hotline for members of the public to report the names of employment agencies supplying staff to the Royal Mail, believing the practice was illegal, despite denials from the postal organisation.

A Royal Mail spokesman branded the strikes “unnecessary and irresponsible.”

The union said it was reiterating its offer of unconditional talks at the conciliation service Acas to try to break the deadlocked row. Next week’s 24-hour strikes will involve 43,700 staff across the UK in mail centres, with network logistic drivers and garage staff taking action on Thursday; 400 workers in Plymouth, Stockport and Stoke who deal with poorly-addressed mail, on Friday and 77,000 delivery and collection workers on Saturday.