Cashing in bonds...
As long as you're not tax-equalised, then:
1) Yes, you should be in a lower tax bracket so you'll save some bucks cashing them in while you're in the UK.
2) But, if you bring the proceeds to the UK, you'll pay tax in the UK on the money. It sounds like you might be in the 40% tax rate - ouch!
3) If you cash them in, but leave the money in the US, you won't pay tax in the UK.
If you are tax equalised, then you will pay standard US tax on the bonds as if you were still in the US. You will not get the benefit of the lower tax rates afforded by the $80,000 exclusion.