Hi Red
I thought you'd had a reasonable set of answers from Dave and Chris.
If anything, Dave's estimates on weight are a bit heavy (ha, ha). None of the Hanson Brick examples here weigh over your own estimate of 3Kg - most are around 2.5Kg.
http://www.hanson.co.uk/assets/documents/Sept% 2006%20Brick%20Technical%20Info.pdf
The skip - I agree that it would all fit in an 8 cubic yard skipo, which should cost about �150 as Chris says.
Some sort of confirmation of this here.
http://www.skiphiredirect.co.uk/skip-hire-pric es.html
(They are never going to put their best prices on the web).
Landfill tax - this shouldn't apply - ask where he got rid of it. As clean hardcore, what he should have done is take it to a recycling centre where it is ground down and resold as aggregate. Commercial people delivering to such sites do not normally have to pay anything - it's free delivery. So �150 should have covered the transport / disposal side.