Gladstone's are the brains(?) behind the Independent Parking Committee (IPC) which is the smaller of the two parking Trade Associations. They also run the misnamed "Independent" Appeals Service for the IPC. And coincidently if you fail to get your IPC ticket cancelled, Gladstone's will issue court claims based on the information provided to the "Independent" Appeals Service.
Gladstone's as a Debt Collector
Here is an example letter that does not come from Gladstone's - identifiable by where the money needs to be sent.
Gladstone's as a Solicitor
You can see this letter is almost identical to the one above save for who needs paying. This version will lead to a court claim within 14 days whereas the other one does not.
Since there is very little money in these claims, Gladstone's mass produce automated claims on behalf of the clients. They are mainly used to frighten people as very few go to court. So if you get this second type, contact the us as soon as possible.
Debt Recovery Plus trying to look like Gladstones.
And for completeness here is Debt Recovery Plus pretending to be a Solicitor too.