If they're extended arches, then (from the pic) not by very much. An ugly fitment which you should consider removing, IMHO! Given that they're not much bigger than standard, you might be able to refit with OEM without too much restoration work.
Might the tyres be "outside" the line of the arches if they're standard? If so, the MoT bloke might have an issue with anything that allows the outer edge of the tyre to extend that far, which might be the reason the PO "fitted" these.
The finish of the rest of the bodywork seems pretty good, which makes me wonder why he/she did this amateur job and spoil it. The arches themselves seem to be thin plastic or GRP - based on the crack - so worth getting rid of for that reason alone. They'll give constant trouble.