Royal Mail has begun the search for a new chairman after Donald Brydon announced his intention to step down.

Mr Brydon was appointed chairman in 2009 and has overseen a period of major change for the company, including its flotation in October 2013.

The process to appoint his successor has started and Mr Brydon will continue to chair the board until at least the AGM in the summer.

Just over a year on from its controversial flotation, Royal Mail shares have slumped roughly 28% from their peak in February amid worries over increased competition.

It is under pressure from the impact of Amazon's increased use of its own network for deliveries, and from rivals such as TNT, after industry watchdog Ofcom said last month that other firms do not have to match the Royal Mail's costly obligation to deliver across the UK for one price.

Last week Royal Mail said its Christmas went to plan after it handled around 120 million parcels during December, a rise of more than 4% on a year ago.

Despite the growth, the company said trading conditions were ''highly competitive'', with UK parcel revenues flat in the nine months to December 28.

Its rival City Link was forced out of business last month amid the fall-out from Amazon's increased use of its own network for deliveries.

Mr Brydon said: "I am proud of what Royal Mail has achieved as a company in the last six years.

"Our transformation is well under way and we are now a FTSE 100 listed company. I feel that now is the right time for me to make this decision."

Mr Brydon spent 15 years at French insurer Axa Group, where he held a variety of senior posts. Prior to that he worked for 20 years at Barclays, where he rose to become chairman and chief executive of its asset management arm BZW Investment Management.

Royal Mail chief executive Moya Greene said: "Donald has played a key role as chairman during one of the most eventful periods in our history. I would like to personally thank him for his support and counsel."