I was with M&S too and same as Bruneep, M&S told me to keep it.
However the police would not hand it over until I got a letter from the insurance company.
I then had some slight fun. The conversation went something like this.
me – ‘Hi Mr M&S, the police have recovered my bike’
m&s – ‘That’s wonderful news’
‘Is it possible for me to buy it back please?’
m&s – ‘Well technically the bike does not exist as far as we are concerned’
me – ‘OK, Does that mean you do not want it?’
‘Correct’.
me – ‘OK then, please can you write me a letter saying that you do not want the bike & are happy for me to pick it up from the police’
m&s – ‘Sorry, we can not do that as it does not exist’
…..
Cutting a long story short, with what must have been a 30 minute call, they eventually agreed to write a letter saying that they gave the permission to the police to hand the bike over to me, but it was worded by some smart arse such that one day (never) they could say ‘Well actually it is ours you know’.
Anyway all ended well, I got my nicked bike back and a brand new bike out of the insurance. Win win.