Manchester United have stressed they will never sell the naming rights to Old Trafford following confirmation present shirt sponsors AON have agreed an eight-year contract to put their name to the state-of-the-art Carrington training ground.

From July 1, Carrington will be known as the 'AON Training Complex' and forms a central part of a wide-ranging deal that also includes sponsorship of United's training kit, their annual summer tours and, for the first time, friendly matches.

As had already been agreed, AON will also become the principle partner of the Manchester United Business Network and also sponsor of the Manchester United Foundation.

No figures are being put on the contract. However, it is thought to be less than the £20million annual sum AON agreed to pay when they became United's shirt sponsors in a deal that will expire in 2014.

However, it will be higher than the £10million-a-year DHL paid to sponsor the Red Devils' training kit two seasons ago, considering the club bought the contract out earlier this season believing they could extract a more lucrative alternative.

"The first phase of our sponsorship was concerned with brand awareness of AON as a commercial business," an AON source said.

"The second phase is about creating a global understanding of the capabilities that we provide for clients around the world."

The deal refutes any suggestion AON have been dissatisfied with their treatment by United, even though the initial sale of the naming rights to the club's training kit appeared to undermine their own position.

In addition, it has already been confirmed US car giant General Motors will have its Chevrolet name on United's shirts from 2014 after agreeing to pay an eye-watering £357million over seven years.

That United have added friendly matches into the new AON contract is intriguing as it means from their 2014 tour, they will be wearing two different companies on their kit.

It merely emphasises the huge marketing tool United have become in an era when televisual advances such as Sky+ allow viewers to flick through normal advertisements in a way they were never able to before.

However, that is bound to trigger suggestions United could try to sell the naming rights to Old Trafford.

Previously though, United insiders have said such a sale would be virtually pointless because, as Newcastle found when they tried to change the name of St James' Park to the Sports Direct Arena, it would merely irritate fans, who would not use the new name anyway.

Even members of United's own staff do not refer to Carrington by its formal title - the Trafford Training Ground - and club officials have been quick to rule out any similar deal for Old Trafford.

"Old Trafford will not be sold," said Ed Woodward, United's executive vice-chairman, who will replace David Gill as chief executive in the summer.

For their part, AON acknowledge that the Carrington name, whilst not having the same resonance as Old Trafford, may also stick.

"We are very aware and respectful of the fact some people will continue to call the training complex Carrington but in time, we hope they come to understand what the AON brand stands for," added the AON source.

"But we feel this agreement will enable us to do something with the club which is unique.

"We have been more than delighted by our partnership with Manchester United.

"Awareness of the AON brand increased from 39% to 50% in the first year of our sponsorship and the percentage of unique visitors to our website have increased by up to 55% on matchdays."