Hire Car from London to Edinburgh and return to London - over 18 days

In late August this is a risky game as it is still peak season, with the schools on Holiday.

When they go back the first week in September things start to quieten down outside of London.

Book your arrival night and departure night at Heathrow in advance, although it is very unlikely you wouldn't find somewhere on spec.

At least in the Lake District you will always find places to stay if you are flexible and have a car, outside peak season.

But don't do this literally as written, turning up and knocking on doors etc. Rather at the start of each day go on booking.com or the websites of budget chains like Premier Inn, Travelodge or Accor. Those three between them will pretty much always produce something for you.

For Edinburgh if availability is tight look across the Firth of Forth in Fife, or down East Lothian in the likes of Dunbar or North Berwick.

It used to be very easy to do this years ago. I spend 3 weeks in England in the mid 90's and found places to stay by stopping at the Tourist Info Center (TIC) in each town, and they would call ahead to my next destination and find a room for me. It was called the Book-A-Bed-Ahead program and was wonderful.

Obviously, that no longer exists and many TICs have disappeared from the smaller towns (at least physically) but as Stuart (isn31c) pointed out, you can use the internet to search for places. I prefer to use Google rather than booking.com, as booking.com only has hotels that pay a fee for a listing, but a lot of people here use it with success. That said, Google probably would show the little places that can't afford booking.com. I found a small B&B on the Isle of Skye that was only £50 a night and very comfortable using Google maps. I would suggest booking directly with the hotel, regardless. I also recommend stays at Premier Inns, which Stuart mentioned. You can find them all over England. They are very reasonably priced, clean with very comfortable beds, and decent sized rooms.

I had a car for a week in Devon and Cornwall last late September and tried your plan of winging it for accommodation, but found it too stressful as after finding several hotels were booked up, and going to the next town and finding the same, and now it's getting late and dark and I'm tired. So I switched over to what ISN31C suggests - booking in the morning online.
If expenses are a concern to you, I also found that many places charge a lot more when you just show up out of the blue hoping for a room. At a Premier Inn in Bodmin, Cornwall, reception told me she could not apply any discounts if she booked me in, but if I just sat in their lounge and used my laptop to book myself in, I would save around 10 percent.

My ego also demands I mention that I'm not generally a nervous traveler and I have done the "keep driving until you find a hotel" on various trips around the US and Canada, but it just seemed less stressful because I guess it's more familiar with the big wide roads and quicker travel, so I was never really worried even if It was late at night.

At a Premier Inn in Bodmin, Cornwall, reception told me she could not apply any discounts if she booked me in, but if I just sat in their lounge and used my laptop to book myself in, I would save around 10 percent.

Ha, I've had that happen in the states as well, where I had to go online while I was at the reception desk to get the lower price.

thank you all for your responses and suggestions, appreciate them.

Just to correct the point about accommodation paying to be listed on booking.com. As the owner of a B&B that is listed on that platform I can say that is not the case. We do not pay for our listing. We pay a commission to booking.com on each reservation.

isn31cs suggesting of booking accommodation on the internet before you set out in the morning is sensible. Although in August small providers are likely to already be booked up.

You won't see many 'vacancies' signs these days and will likely waste a lot of precious sightseeing time driving around looking for a bed for the night.

We do not pay for our listing. We pay a commission to booking.com on each reservation.

Jacqui, thanks for the clarification. I knew there was some sort of payment involved but should have checked to see what kind before I spoke. 😊

No worries Mardee!