Thank you everyone for your positive replies - exactly what I was hoping for.
In my case, it's relatively simple in that it is our family home that we decided to rent whilst living in quarters a long distance away. We are not in the buy to let business and will move back into our house at some stage over the next few years. RBS who my mortgage is with, have no problem with SP doing this and my mortgage remains exactly the same as it was. I have had to register as a landlord and my buildings and contents insurance package has been changed to 'landlord' insurance which cost about 10% more than normal.
The rest is in the hands of the Letting Agency and I will just have to see how that works out. They were not very helpful on the tax questions I had other than telling me that I had to tell IR that I was renting. They also said that because our mortgage was in joint names, I couldn't rent out the property in the name of Mrs PA only. As Mrs PA is currently a housewife, I thought that may have been a way to reduce the tax burden?
Bottom line though and following the good advice above; keep detailed financial records of every transaction involving the house and find a good beancounter to dot the i's and cross the t's.
Thanks to all....