Advice needed - Disclosure of employment changes to Home Office

[bammargera]

Background

Application and biometrics done mid November 2017. Docs returned late December 2017. Mid February, email reviewed with five working days notice to send bank statements as couldn’t see my salary credits. No idea what happened as salary clearly in all statements, probably lost them. Sent back statements to them. Now been 15 working days and heard nothing. Very annoying to say the least as we had a thorough and good application and they clearly lost our information and now we are still waiting for over 15 weeks.

Complication

I’ve been headhunted for a job representing a large increase in pay and also a very good career opportunity. I can’t turn it down and I’m handing my notice into my work this week.

I understand that, as our application is still under consideration, I just notify the home office. My questions are:
How? (Email/letter/phone)
What? (What do I send them? I have a signed employment contract with the new employer. Do I also need letters signed by their HR etc?)
When? (If I hand my notice in this week, do I have to notify them immediately given I still have three months notice in my current job and therefore will still be working there until into June?)
Impact - given we have already waited 15 weeks, had a bad experience with HO losing documents submitted as part of an extremely thorough application, I’d be gutted if notifying them of a change in employment lead to a whole new round of document submissions and bueraucracy. How much longer will this add to the application time or is it a straightforward cSe or notifying HO and then moving on? Given it’s been 15 days to apparently review my bank statements for clearly identifiable salary amounts I’m not hopeful.

Thanks for reading