Just got a quote of £60,000 for a 30m2 ground floor + 10.5m2 upstairs
extension, which I think is a bit steep! I'll get more quotes but even
so I've decided to dig my own foundations by hand and lay the concrete,
to save money.

My existing house is built in the bottom of a former limestone quarry.
The top-soil/clay is relatively shallow approximately 500mm, below that
you hit solid limestone bedrock. So it's quite good for building solid
foundations on.

Digging the trench I think will be relatively straight forward
(architect's plan state strip foundation 600mm x 200mm)

I have a number of questions and concerns:-
My biggest concern is making sure the concrete will be level and
uniformly at the same depth (digging the trench to a uniform depth is
relatively easy). I've read about knocking wooden pegs in to the
trench bottom so you can easily gauge concrete levels. But won't they
weaken the foundation if left in which I'm told you do? How about
using Steel pins, where do you purchase them, are they the ones used
for steel reinforcing?

-How do you tamp the concrete easily without sideboards do you use a
"vibrating poker"?

- Should I measure concrete depth to coincide with brick/block
measurements, so that the once the bricks are built up to ground level
they coincide with the existing house brick level?

Any tips websites, books that can give me a full insight into what is
required would be most appreciated.