Shimano Chainring Set
While cleaning I found the part number printed on the inside of a crank handle. It is a FC-M191. This part seems not to be available in the UK anymore so I decided to buy the MC-M411, which has the same teeth number for all three cogs, is suitable for 8-speeds and has the same Shimano rectangular axle fitting as the FC-M191.

I also bought a Tl-FC10 crank pull to disconnect the cranks from the bearings.

It appears that the derailleur is an Altus but other parts have been used for the Chainset in the front. This makes it difficult to find the matching parts.