Train Tours in Britain

Well I Googled it and found absolutely nothing.

The company is McKinlay Kydd, not as the OP wrote

I've never heard of the company and they don't get mentioned on the travel forums. However they do get very positive reviews on AIT

If you click >https://www.aito.com/aito-members - you will find that they are ‘members’ of aito so presumable they have paid a fee to join? You will also notice that all the other members also have excellent reviews.

The train tours offered look good.

AITO is a very well respected organisation of small travel operators. I know nothing about McKinlay Kidd but have used a number of other AITO operators in the past.

Looking at their website they have some interesting tours, both guided and self-guided. They seem to move at a sensible pace with many 2 and 3 nights stays. I would have thought that they would be a useful option for any visitors from overseas that don't want to drive themselves.

Having looked at the website I see no red flags, in fact the itineraries look quite good to me. Being a member of AITO is a positive, and the prices are not out of this world.
On paper a general thumbs up