Presuming you are mobile, with a rental car, you might consider the Travelodge option which my mother and I have used a number of times, with great success. American style motels (rooms bigger than broom closets, modern bathroom), these tend to be located on the outskirts of the major centres dotted across the UK. Rate last time we did this a couple of years ago was 32 pounds 50 double per night, but no doubt this would be 35 pounds now. In May you can do what we did -- find a Travelodge in an area you wish to explore and book it for however many days you want to stay in the area. At the same time, the personnel at the place will book you to the next Travelodge adjacent to the next place on your itinerary and if it is booked will find you an alternative choice. So long as you book a few days ahead you will be OK in May -- except if you are there for a Bank Holiday weekend (one in May). Then you can expect to shell out big time for an unbooked botel, or sleep in the bushes!

If you haven't made too many plans already and a frequent surfer of the net..don't overlook guest houses. They are friendly and include some meals.
I stayed at the Argyle Hotel in Glasgow and had a wonderful time. Its near the University but within walking distance of the Art Museum.
In Edinburgh I stayed at the Balquihidder Guest house. Once again, friendly personal service
B

Your idea of stying in B&Bs is great. My family stayed in B&&s last July and Aug. all over Northern England without reservations and had a fantastic time with no problems. Go to pubs and ask where they might recommend a local B&B. They probably will call for you to see if there is availability. By the way the food in the pubs was the best we had any where in England.
We prefered the Farm B&Bs to the City ones.

please tell me more about the guest house in edinburgh as i will be there next week with my wife and 10 year old.

B & B is the way to go. I have done it several times through the highlands and lowlands of Scotland.
In almost every town there is an information center. They are marked with an "i" on your maps. Each info center has a list of B & Bs in the area and will call to reserve the room for you (cost usually 2 pounds). They will also call the next town to arrange a room for you. Its the greatest!! Remember, they close at 5:00 pm so stop fairly early
to make your reservations or there may not be any left.

B&Bs are the cheapest way to go, but always ask to see the room first, also ask about the house rules, some places wont you in before a certain time, ohers let you have a door key. expect to pay around £16 per night each about $20.
If you are going to the lake district or Scotland stop off at Marchmain Gueat House in Carlisle, its only 2 mins from the freeway great people run it and make you very welcome, they even do your washing if you ask them.
Telephone them early on 01228-29551
you wont regret it

Hi--There is a really great bed and breakfast just outside Sterling...it is called Lowefield's and is run by a couple who really care. They have a website. My wife and I stayed there just about a week ago and we were so pleased. They are located about 35 minutes outside Glasgow. You are in the middle of both Braveheart (Sterling) and Robert the Bruce (Bannockburn) areas...