Estate agents ? builders ? former owners & tenants ? no one will be suspicious if someone is entering with a key.
Most insurance companies state this is required so please check with them as you do not want the double whammy of being broken into and then not being insured.
Again with insurance companies most require all external locks to be British Standard.
In all our time in the locksmith industry we have only seen this a few times so is quite rare but please do not take the risk if you would like to fit the locks yourself and just require some advice please feel free to call us as we will be happy to help.