If I may correct the second poster, it wasn't any specific band.
Yorkshire co-op band used to do the job as a regular part of their itenerary. I was associated with the band in it's former guise as a full, contesting brass band for many years and performed at several notable sporting occasions with the band, including this one on several occasions.
A few weeks ago, there was an announcement on here from an individual who had obtained the contract from the events company to provide the band for the event and was inviting applications from individual players interested in playing.
They would then assemble a group of players (though to use the term 'scratch' band may be unfair and not entirely accurate) to perform at Old Trafford in order to fulfil that contract.
There were former members of Yorkshire Co-op band as was in there though, plus members of the training band/Mode For academy band.
I was there. The band was made up of a few ex coop players and then players from the likes of tredegar, reg vardy, harrogate band and a couple of others. It was basically on a first come first serve basis and it was an unbelievable experience!! Out on the pitch in front of nearly 72000 people, the noise from the crowd when the teams came out was just immense.
I was also there, though I was wielding a guitar in Diana Vickers' band............I can second the comment on the noise / experience.....awesome.
The brass band did sound very good.
I've got a small amount of footage on my iphone of the soundcheck with Rhydian.
If it's the same as previous years where there has been a tenor vocalist, it would be Simon Kerwin's arrangement. If I remember correctly it's up a semitone from the normal band arrangment (into brass band E/A major) to make it sit better with the vocalist.