happy to be corrected - but I think crying that you aren't taxed on a lump sum if you bring it with you when you arrive and therefore it's not here in the UK earning for you ifykwim. A quick google found the below and I'm very hopeful it's correct as we are making the move home some day and while we are in the UK we are busy saving!
^Will you be taxed on the money you bring?
This is a common question, and the general answer is NO, unless you don’t bring the money with you at the time that you migrate. Even then, the only tax you will pay, will be on any increase in its value since you became resident here. This change in value can be just from the Exchange rate movements, or the interest you have gained from Bank Accounts in the UK, or even property value increases.
An example to try to explain this:
Assume you have a property in the UK valued at 100k, and 20k in the bank.
You move over when the exchange rate is say 2.4 to the A$, therefore you are worth $288,000.
Assume you bring your funds over 3 months later and the exchange rate at the time is 2.45 to the A$.
You bring 120k x 2.45 = $294,000.
Your worth has increased by $294k – $288k = $6,000 and this is the figure that is taxable as part of your income for the relevant tax year. If the value of the house had gone up or down it would affect the taxable figure accordingly.^