My opinion only.
You cannot get work in an airline or any charter company without an IR. Your exam credits are based on you getting it sooner than later as well.
From the GAPAN website it appears airlines are expecting you to turn up with an MCC as well. (they should pay for it but they won't while they don't need to).
Your type rating is only "current" for a year. After that, you'll need to do an LPC again. (You do an OPC after 6 months, and an LPC after 12 months). (I am not talking about the rating validity which is 5 years - UK CAA). So if you do a rating and fail to get a job, you'll have to budget that cost too. Which is a lot more than a piston IR renewal.
If I was you, I'd get the IR done asap, tack on an MCC when you feel like it and then do the Instructor Rating. Timing is every thing. The weather can make or break you in the UK. From what I understand, the instructors are being employed. If you're on a field that has some bizjets, say hello and see what they want to be hired. You might be pleasantly surprised.
Get some hours and experience under your belt all the while sending off CVs to various airlines.