Because of this, and you don't usually say 100k mortgage + your deposit. A mortgage you usually say 100k of which you'll put x down.
I must have misread that. In the OP (as I quoted) it looks like he's asking about a mortgage (borrowing) £100k. But the post you quoted seems to indicate a total value of £100k, with a deposit of £30k - so only borrowing £70k.
This is why I usually try and answer as I did, rather than just linking to calculators, as some people get confused about what numbers to enter into the calculator.
If he is only borrowing 70k, then (again assuming 25 years):
Assuming 2.5% interest; you'd pay back roughly £315 per month and £95k total.
Assuming 3% interest; you'd pay back roughly £330 per month and £100k total.
Assuming 5% interest; you'd pay back roughly £410 per month and £125k total.