Hi David. I'd say that advice from the travel company is a load of cobblers! If you are travelling to Spain with a return ticket in September, I GUARANTEE you will have no problems, given the circumstances you have outlined. Unless you intend to stay until April that is!
The Spanish Tourist board website says "British citizens may visit Spain on production of a valid passport. No further formalities are required."
http://benalmadena.homestead.com/map14.html

Normally what you are saying is correct tonyadams78 but there are some travel companies who have that rule for travelling and if your passport does not comply with their rules they will not let you fly.
You can apply for a new passport and have the passport dated from the time it would normaly expire. Further information and advice can also be found on the Passport Office website (click here), including details of online renewals, passport fees,
processing times, etc.