That said, from an employers perspective, I'd be wondering why if you felt this strongly and were than unhappy you didn't voice these concerns. Perhaps they were and were ignored?
Yup, as I said above I raised my concerns a few times and it was always met with a non-committal "we'll see what we can do".
Had a long chat with my manager yesterday, and while he was eager to keep me, he wasn't able to alleviate my concerns that the situation wouldn't improve in the near future.
The offer was basically to beat the raise by 25% (so 18% in total) and bring me back into the office, although there wasn't really any clarity on what I would be working on.
So... I declined and gave my notice.
Having (unsurprisingly) thought about it a lot over the last couple of days, I came to the conclusion that it would be silly to pass up on the opportunity, especially given that if I stay there's a strong possibility that I'd be in a similar situation in 6 months.
Staying with the current company may be the best thing to do in the short term (e.g. a couple of months), but I think more important is how I'm going to feel 6-12 months down the line when I've completed my probation, potentially had a payrise at the new company (which TBH I would be unlikely to get at the current place if they bump my pay up now to match), and am doing something I enjoy (hopefully!) with plenty of scope for progression.
Ultimately I guess I won't really know for 6 months+ whether I've made the "right" decision, but looking at it as objectively as possible, I think I have.
Bear in mind 600 miles commuting each month will come with a cost, not just in terms of motoring that will eat in to the raise (no longer cycling, though 12m is easily do-able depending on the route) but also an hour out of your day.
The fuel cost isn't a massive amount, 600 miles is a 1-1.5 tanks, so about £60-80. The convenience/time is a bit more of a factor, but then I guess it's only an extra ~15-20 mins each way, which is worth it for having a job I actually want to do! (And is a vast improvement over the 1hr+ each way I'm doing at the moment).