I assume the car spares shop has incorrectly sold me some NGK ZFR6T-11G 5960 plugs which appear to be for the 1.4 according to the Haynes manual.

 

The old ones that I changed previously and kept are ZFR5P-G.

 

What my real question is, what effect does the gap have, in other words if it's 0.75mm instead of 0.8mm will it advance the timing and thus 'help' a high mileage engine? I notice the original plugs I took out a couple of years ago are more like 0.9mm gap. 

No, gap does not affect timing, gap is set to suit the energy output of the ignition system, a higher energy system can spark across a larger gap.

14 hours ago, LesCM19 said:

ZFR5P-G

Those suit the BMD (6-valve) rather than BME, according to the catalogue.

These are the suggested ones, bottom 4 part numbers are all options for BME:

 

All BME ones except the economy one are superseded by 101 905 617C, but it doesn't say anything about them.

Edited 6 September, 20241 yr by Breezy_Pete

101905617C comes up as what they gave me, NGK ZFR6T-11G according to various websites, so I guess I'll go with that.

Well, the car certainly likes those NGK ZFR6T-11G plugs. It also likes the middle plug not being hand tight with brown soot escaping anymore, judging by the coil on that cylinder (replaced). Will whip that one out again in the near future, clean the recess & plug seat for good measure but so far so happy.