There are only 2 types of buyers to buy this:
1. Teamviewer GMBH - The owners of teamviewer.com
2. Someone who thinks they can make a profit by re-selling it to Teamviewer GMBH
It is more likely that it is the 1st one.
It is worth noting that Teamviewer is a registered trademark here in the UK since 2005, whereas teamviewer.co.uk was registered in 2006. This is not a great standing for you.
However. They have come to you, and presumably made an opening offer. Whilst this could be used as evidence in a DRS case against you (I think) the odds are that they are willing to forego this hassle if you take a reasonable price.
Looking at sedo I don't see a 'make offer' so presumably they have hired a sedo broker or similar? Which means they are willing to pay a premium for the domain.
I would say low £1,xxx but be willing to accept high £xxx
Good luck