Not what you want to see!

[DIYDad]

Looking at the bark (only a thin strip so this is purely guesswork), I think:
Not Oak
Possibly wild cherry but cherry bark is often more orange or brighter
Maybe worth throwing Mountain Ash/Roman into the mix if it’s been growing in the UK
None of these thoughts are from woodworking experience and it is more years ago than I care to remember that I studied horticulture so not 100% reliable there either!!

 

[Yojevol]

Having just searched thru my book 'Tree Bark, A Colour Guide" by Hugues Vaucher, I agree it's probably not cherry. The only one of 560 photos which was a possibility is sycamore which, in this circumstance, must be a possibility.
A search on the net came up with the above photo from paulkirtly.co.uk
Brian

 

[DIYDad]

Yes I thought Sycamore might be a possibility too but got to the overthinking stage of older tree bark is more scale-y. As younger (relatively) trees have smoother bark Sycamore might be more likely?

 

[Oakay]

Another vote for sycamore. Very prone to furniture beetle too.

 

[Sean Hellman]

Looks more like beech to me and wood worm love it. You can get worm in oak heartwood occasionally especially some to the hybrids, but you will not see it totally eaten through like this.

 

[Sgian Dubh]

You can get worm in oak heartwood occasionally especially some to the hybrids, but you will not see it totally eaten through like this.

That's not the case. As I said in my earlier post oak can be riddled with tunnels excavated by the grubs of common furniture beetle - it can take many decades and repeat infestations, but it does occur especially in unheated and relatively damp buildings. Oak is not the favourite food source of the common furniture beetle, but if that's what is available they'll munch on it. Slainte.

 

[Essex Barn Workshop]

Beech would make sense, there were some smaller pieces of beech within the barn. No cherry was mentioned, and I don't think it's sycamore!
Whatever, it's firewood now!
Thank you all very much for the responses, and keep them coming.