Last stupid question I promise! Im soon going to London and have a 1st class Britrail pass for some of the time. While I know my itineary (day trips) and will make departure reservations, I'm not sure how long each day i'll visit (I'll be in Bath and Salisbury for example)and wonder if it's in my best interest to guess and also make reservations back to London. In other words are there non reserved 1st class seats in British trains or will I usually be able to find a seat?

There is frequent service on both the London-Bath route and the London-Salisbury route. You won't need to make a reservation. Just get on the next available train.

Sugguests you are visiting Stonehenge. If so do take time to visit Avebury (where you can touch the stones) and Salisbury Cathedral.

http://www.wdbus.co.uk/htm/ta/sdo-stonehenge.asp

You might also find London to Salisbury to Bath, overnight in Bath & return to London the next day is a good option asd it's only an hour from Salisbury to Bath (or do it the other way round)

alanRow makes a very good suggestion. Instead of a long journey to/from Bath only to turn around and repeat the exercise for Salisbury/Stonehenge is a big time waster w/ such a short trip.

Consider London > Salisbury/Stonehenge/Avebury . Bath > London w/ an over night in Bath. You'll see a lot more and spend less time on trains.

Many thanks for providing relief from anxiety!!! They are good suggestions. In fact, I just found out the the Bath fringe festival will be going on when I plan to go so one trip for both might make sense.