yes, that's true. Your new lock is a British Standard which is very strong, and has upgraded fittings.
But if you have, and can use, a drill and chisel, the new one will fit.
Edit
Do you know anyone who does? You need a careful and experienced person to do a neat job, but it is straightforward for a person who can do woodwork.
If you have to hire a carpenter (no need for a locksmith) I don't know what it would cost. Possibly their minimum charge.
BTW "24 hour locksmiths" who advertise widely are notorious for high charges.
p.s.
A British Standard lock, like the one you have, will probably meet the requirements of your household insurance. A cheaper, weaker one will will be easier to fit but almost certainly won't.
is there any sign of another lock having been fitted to the door, especially a mortice lock?