Detainer style locks provide a higher number of key combinations than lever locks
The Chubb brand is now owned by Union. To get a locksmith to replace these locks you can expect to pay around £200. The locks are some of the most expensive on the market.
If you have lost the keys for your current lock, it may be worth asking the locksmith if they can make new keys or put a new lever set in the lock. Prices for this may start from £65 upwards if y0u bring the lock into the locksmiths and £95 and upwards for a callout.