The magazine industry has also voiced concerns over the changes, which would be implemented in September next year. The large letter size will affect magazines and DM with first class prices set to rise next year from 28p to 46p. Second class items will change from 21p to 38p.

"This has been discussed for a few years and the plans do not reflect the way the DM industry has developed. It will have a negative effect and in terms of large-sized mail, it is a tax on creativity," said DMA director of industry development and postal affairs David Robottom.

The biggest losers in the magazine sector are likely to be A3 B2B titles.

"We are concerned the Royal Mail's plans could be flawed by using measures for pricing that involve subjectivity," said PPA chief executive Ian Locks.

The postal regulator Postcomm has announced a three-month consultation period and prior to the announcement Royal Mail had two years of discussions with the PPA and publishers.

Haymarket Group has recently reformatted its PR Week and Marketing titles from A3 to A4.

"Haymarket is neutral on this as we have a wide portfolio of titles but more lobbying needs to be done," said production director Chris King.

Story by Philip Chadwick