Easy. They are not suitable (offer to buy the alloys cheap).
Any 200TDi defender will probably not take factory alloys wheels at they don't fit the hubs properly and the drive member sticks out through the centre hole.
If it's a 300TDi or has had the hubs replaced (alloys wheel studs haveeither a "-" sign or a triangle stamped on them for a start) then any Disco/RRC alloys will still not be load rated for a 110.
This leaves aftermarket alloys. You should be able to find load data on the inside of the alloy casting, then check your handbook for max axle weights etc.
If the info isn't there play it safe and don't fit them. Post a pic on here and wait for advice, someone will know.
Meanwhile the tyres may still be suitable, the load data has to be printed on the sidewall, if in doubt again ask here or approach a reputable tyre depot for advice. They may refuse to fit tyres that are more than 5 years old though, again it's the law.