I see that Staines is very close to Surrey and suppose to be in Middlesex so don't really know why Ancestry has county as Surrey.
Linda,
The kind answer (kind to Ancestry) would be that Staines (or Staines-upon-Thames as it has rechristened itself

) is in Middlesex. However, since the local government re-organisation many years ago which created Greater London, Staines came under Spellthorne Borough Council, which itself is under Surrey. So for local government purposes Surrey is the right answer, but in reality it is Middlesex.
The more accurate answer is that Ancestry's indexing is......shall we say interesting and displays a lack of knowledge of the area or willingness to check.
<<climbs down off soapbox>>