If I remember, Tiggs, the house has an annex? Not a very small property then. So I guess that 500 is about right for south London.
Cheaper elsewhere of course.
For a surveyor, preferably go for someone you know, or can be recommended. If not, go for someone from a "proper" firm that can take the responsibility. In the end, they're all RICS registered anyway.
I have to agree with Auntie here. (Well, I would say that, wouldn't I?) A long established local builder would be ideal. 1970s housing is usually quite predictable. Modern Building Regs were starting to come in properly. Except, naturally, levels of insulation were nowhere near today's for example.
Still, they tend to be well built, if a tad "unimaginative" in design etc.
70s houses rarely hold any surprises for an experienced builder.
At least there will be no faffing about with hopelessly misleading damp meters.
Surveyors often make more trouble than necessary, since they have to be "seen" to be thorough. Often, what a surveyor might flag up as a fault, a builder would deal with as a triviality.
The only advantage with a surveyor is that they carry substantial Indemnity Insurance if they should miss something major.
A builder would likely just have his Third Party Liability insurance.
I wouldn't worry about that though.
Perhaps your Dad might know of someone.