The quicker the better.
Why not knock-out the PPL / IMC in 6 months over the summer (funds permitting)?
As you say, structure your hour building and do some long navs (UK-Ireland / UK-France / UK-Holland you get the idea. 100hrs P1 could be done in a month if you really wanted (5hrs a day Mon-Fri), make it 3 months and enjoy it.
ATPL's in 6 months if you can (full-time). Look at 4-5 schools for the flight training. Bristol may not suit you (I have heard a few bad words, but then most schools have those). Try and spend a few hours at each one to see where you fit in best, as they are all very different.
PAT Bournemouth are very good. Great SIM (very important) and very professional.
OAT made me shiver, as did Cabair (sausage factories).
Avoid Cranfield.
Look at the market nearer the time for the TR. You may find that Instructing opens more doors than a TR with no job at the end (6.5K).
Storm Aviation will give you time on type, but no job for 25.5K.
As for Distance Learning, I am not a fan. The majority of students give up within a month and go full time. Re-mortgage and just think of the money as funny money - or it will send you nuts.
Good luck and keep looking forward at the next hurdle. If you take small bites at this, nothing will stop you, but if you look at the bigger task that you have to complete too soon, you will only get overwhelmed. At 40, you bring stability and life skills to the table. The good operators will see this.