Locked out in
Derby?

Derby was built twice, and the two halves need different locks. The first is the railway: the 1840s workers' terraces around Railway Terrace are among the earliest purpose-built railway housing anywhere in the country, and the Midland Railway cottages on Highfield Lane in Chaddesden went up in 1868 to 1870 for men at the sidings. Where those still have a timber front door, the lock is a mortice, and BS3621 is the standard that actually applies to it.

The second Derby is the factory suburbs, and it is euro cylinders throughout. Chaddesden, Allestree, Mickleover, Littleover, Spondon, Alvaston and Sinfin are largely interwar and post-war cavity-wall semis and detached houses built for railway-works and Rolls-Royce families. Nearly all of them have replacement uPVC or composite doors now, locking with a cylinder through a multipoint mechanism.

Know which of the two failures you have before you pay for anything. A handle that will not lift, or a door you have to lean on to lock, is the gearbox inside the mechanism — a repair, and a much smaller bill than a door. A cylinder standing proud of the handle plate is a snapping risk, and a TS007 3-star cylinder settles it.

Derby is the far end of my patch and it is still the same price — no zone pricing, no mileage, the published figures quoted before I set off.