I've just switched to British Gas for gas and electric ( Collective
Fix December 2016 via Money Saving Expert Cheap Energy Club) and I may
get the option for their Smart Meters.

If I go for this option is this likely to make it difficult to switch
to another supplier in a years time, eg. they say that they can't use
the BG Smart Meters? Also, do these smart meters still allow me to
take my own readings for consumption?