Think it depends on the lender? I spent many years working on contract (in fact its the reason I didn't apply for years, I had a perception that I wouldn't be accepted) and had colleagues who told me that via brokers there were lenders who were willing to accept more mobile applicants. The thing in this case is that the borrowers salary is significantly increasing.
Firstly I would discuss with the lender before giving a yes or no answer on the job. You at least will know how they feel about it.
Secondly, if you are able to command confidence enough to get a job offer with a 25k increase (congratulations on that by the way - its an enormous increase) you probably will get similar offers in the future even if you skip this one due to your mortgage application.
Lastly, if you do take a job earning 25k more, you can borrow a whole lot more in future...you could increase your savings by 25k over two years ON TOP OF whatever it is you are saving now.
Have a good think about it - chances are, I'd say you have the skills and experience to get a similar offer even if you don't take this opportunity.