Hi Gjf
Can't help on the guides part but from googlemaps it looks like your hotel has close access to an extensive swathe of countryside, a mic of woodland and fallow style grasslands that look to be open (or well used) by the public. These seem to be some ponds around as well.
Go South West (London Road) to a minor cross roads and turn right along Park View. this looks to be the closest route in. Or, walk a bit further to Church Road (on the right) and then again, turn right onto vicarage Road. This should have a few opportunites to access the counryside.
Alternatively check up Lightwater country park about 2 - 3 miles away or Chobham Common about 4 -5 miles away on the internet.
I don't know of you will have the use of a car or what the public transport facilities are like - Of course the hotel will call up a taxi or two if you don't want to walk to get to these places
I am sure you are aware that afternoons can be a quiet time for birds but you ought to be able to get a list of a 30 - 40 species. Read up on British birds as best you can as there are a lot of look-a-likes. If you can get a bird song CD all the better (if no one comes forward as a guide)
Also worth noting is, in the places I mentioned, there could be dog walkers, lots of.
Having mentioned all the above please be aware that although I pass close by them most days I have never been to those sites. If you don't get any guides come forward I might try to get the afternoon off work for that day and meet you but not as a 'professional' guide. We can see about that nearer the time.
Do you have any target birds?
Steve