The distributors of incandescent filament lamps *are* fully aware of the
*notionality* of the UK's "230" volt supplies and the need to supply 240v lamps that *actually* match the *actual* local supply voltage used in virtually every region of the UK. That's why, if you bother to look closely, you'll find them marked as 240v lamps.Unless your particular electricity supply *is* set to a *nominal* 230v rather than the nationwide 240v used almost everywhere else in the UK, any such lamps marked as 230v ought to be returned to the supplier as "Not fit for purpose".
On the one hand, they'll have a higher efficacy but on the other, they'll suffer a shortened life as a result. This may or may not suit your needs but is the reason why tungsten filament lamps are so tightly specced to the voltage of the supply in and around the locality of the retail and trade supply outlets.