'Towers' are set up so that a company can provide different services - such as desktops, networks, applications - across a whole organisation, which can be provided by different suppliers, but are all typically managed by one company throughout the implementation process.

This is the approach the Post Office is taking. It said: "The model chosen allows the provision of service towers being managed by a service integrator. In this context, Post Office has commenced a procurement to identify a prime supplier to act as such a service integrator and now wishes to seek further prime suppliers to support delivery of technical services through the service towers."

One of these 'prime suppliers' is being sought to provide data centre services, with a contract worth up to £60 million over seven years.

The other prime supplier being sought will provide end user computing services to the Post Office, where the contract is worth up to £300 million over a possible six-year period.

The contract notices said: "The selected bidder will be required toenable transformation of the Post Office's IT estate and be ready for transition of the above services from the incumbent suppliers, as well as providing any new services that Post Office may require in the future, and support all these services as per the agreed service levels during and post transition."