I want to bring mortgage arrears up to date. My question is if I fall behind in payments in the future will it still take 2 years before bank can take action, for example if I started to fall behind in 3 months time.
First of all, if you can clear your arrears you should do so. The sooner you do it, the sooner your credit record will become clean.
Where are you getting the two years from? The lender can start calling you immediately.
If it's your family home, they must treat you via the Mortgage Arrears Resolution Process but when that is over they can take legal action. I don't think it will take them two years, although, in practice they prioritise the bigger and older cases.
If it's a buy to let, they could probably appoint a Receiver immediately.