What to do with £12,000?

Dekota

I see this thread is digressing.

OP: The amount lost in interest to you over those years that you didn't invest is relatively big.

In your case, I wouldn't touch property. £5760 would go in an ISA, £2.5k x 2 in Flexdirect accs @ Nationwide, £750 in Halifax Rewards acc (Could use the switching service to collect £100 bonus), £490 in a vantage account combining with the balance in halifax from time to time to bounce around accs to fulfill deposit requirements of flex accounts.

Potentially, you'll get in interest for 1 financial year, assuming a 2.5% ISA:-

-£144 from ISA
-£245 from flexdirect accs
-£100 from Halifax switch
-£60 in interest from halifax
-£15 accrued in a vantage account bearing £500

Giving you over £550 in interest by the end of the financial year. I would advise for the second year to max out your personal ISA allowance again by transferring balances from all other accounts, equalising all your remaining balances between the other 3 accounts in which you would deposit money in from your income.