As long as you are moving to a good area - even if further out - then yes it sounds a good idea.
The good parts of Central London as you say are shielded to a certain extent from the rest of the housing market - but so are some of the leafy suburbs - eg Richmond or the stockbroker belt in Surrey where there is still plenty of demand from high net worth individuals/overseas buyers.
I would seriously think about a longish fix. I am just in the process of remortgaging to a 3.79% 5 year offset mortgage. I think rates will go up faster than expected - perhaps 2.5% by end of next year. Today's inflation figures were pretty dreadful and rates could no rise as early as this May by .5%.