Thanks, folks - these comments and memories are great! In spite of some of the more (very) cautionary tales, I'm still keen to go back when we can.
However, I'm shocked at the people saying they go to the Premier Inn! I don’t blame you, as you know what standard you can expect, but to me, going to Blackpool and staying in a PI is like going to Rome and eating at McDonalds!!
I know they’re probably desperate to get anything, and it’s a bit of a vicious circle for them, but a B&B advertised at £12 each a night isn’t really hiding what you can expect of it – unless they’re looking for families of 5 or 6 to fill each room. Even so, the cost of the breakfasts, washing the sheets etc. will cost them more than that – and that’s not including the central overheads like business rates, utilities, TV licences, cleaning products and probably loads more. Most of them don't employ staff, but they still need to scrape a living for themselves.
There’s also TripAdvisor which, whilst obviously not 100% accurate or objective, will give you a general indication of what to expect.
We actually went there for part of our honeymoon (I know!), and I still remember researching where to stay (with brochures from the tourist board back then, the web was very much in its infancy). There was one place with lurid Rocky-Horror-style colours on the outside that advertised a great 24-hour party atmosphere with a full bar and their 'legendary' burgers and chips available at 3am. At the other end of the spectrum, there was one that actually said something to the effect of “If you’re looking for a fun place to stay and have a good time, this is NOT the place for you!”. They charged £10 to use their car park every ‘session’ - i.e. if you wanted to drive out anywhere, you would have to get them to raise the barrier and let you out – and then, when you returned after however long, you started to incur the next £10, even if a few times in the same day. Maybe they were terrified of accidentally getting bookings from people expecting the first place! Unless they were using the B&B as a cover for a money laundering operation and actually getting any guests booking would have them instantly rumbled 
Needless to say, we found a very nice place that was somewhere between the two. It was lovely, although the hostess was constantly going on about Funny Girls (the drag show) and urging guests to go. I presume she must have been on commission or had a friend/family member working there.
We might be unusual in this, but we actually like the old-fashioned look with style and decor from decades gone by and harking back to the glory years of the British seaside B&B - as long as they're clean, of course. Modern places are really not our thing at all. I don't if that makes us very weird, or if anybody else feels that way too?! That said, it's still nice to have modern facilities (en-suite and wi-fi etc.) and not just have to be content to be impressed by the 'shaver point and COLOUR TV in every room' advertised proudly on the boards outside 