Thanks for the information. That's a shame as it would save about £1300, but I guess if it was possible everyone would do the same. I assume that I can still start/end a RTW route from anywhere just so long as I purchase the ticket in the UK (at the UK price), or have I misread the rules?
You can start anywhere you like, but that doesn't mean that you can have that ticket priced in Sterling and issued in the UK.
So I thought better than to ask if by starting in a different country then do I pay that countries' RTW fare level price.
Yes, of course. But you will find that the various fare bases are priced at the same price for many countries. For instance, whether you start in the UK or in any country using the Euro, you will probably find that the same price level is applied.
If you want to get a cheaper price, you would probably have to start from somewhere much further away, i.e. some African or Asian country, for example, where the fares are priced cheaper.