Best way to keep rats out of cellar ?

I live in a victorian terraced house with a mini-cellar i.e a 4ft high space under the ground floor. It has no proper floor and can't be increased in height. Rats have dug through the lime mortar under the bottom brick course. They haven't been a serious problem yet but have eaten vegetables stored in the cellar. I've put the veg in a rat-proof container, but I'd like to stop the rats coming in. I don't want just to re-mortar the hole, I'd like to cover the floor with a galvanised wire mesh which goes part-way up the wall so that even if they dig through the mortar they can't get in.

Please help IF you have relevant experience, I don't want to know what people THINK will work, I want to be confident of success before I buy materials & start work.