What else should I be considering for managing large-ish amount of cash?

calathea

As of October 1st 2007 I will have a lot of cash to manage over a period of 4 years, as I am leaving corporate life to do a PhD.

I'm selling my house (which is in a different city I don't intend to return to) and getting out of my mortgage, which (fingers crossed) should net me about £40k after fees and moving costs. Other than the mortgage I have absolutely no debt.

By October 1st, I will have other cash savings of £25k. I anticipate being able to add a further £15k to this sum over the next four years. I don't believe I will need to take the interest from the savings as income, so I will also have the compound interest.

I would love to walk out of the PhD with £100k in cash towards my next house purchase, but I have at least a £15-20k gap that I am unlikely to be able to fill by just earning more or penny-pinching (I am not a big spender, so I haven't much "fat" in my budget that I feel happy about trimming).

My current savings sit in, variously:

1. A maxed out mini cash ISA.
2. A high interest instant access account (which I am about to come out of as the bonus period ends in April).
3. A Lloyds Monthly Saver.
4. A small sum in an instant access "emergency" account.

I had planned to just dump my lump sum from the house sale into whichever high interest instant access account I replace no. 2 with, but I am wondering whether there is some other combination of savings that would work more for me, or products that I am overlooking.

Any thoughts on how I can make my money work harder for me? Buying property is not an option until I am no longer a student.