DJK,
Re the cost of cable and MCBs, from my last post above:
2.5mm twin-&-earth cable runs about £15 per 100m drum, typical domestic type-B MCBs about £4 to £5 each.
If we look at the extra cost of a larger panel (consumer unit), it adds very little. For example, in my usual supplier's current catalog a Wylex insulated NH range 100A panel is £16.29 for the 5-way version and £24.69 for the 14-way (plus VAT). MCBs for this particular panel are £4.59 each, or down to £3.79 each in larger quantities. As you mentioned, compared to the other costs involved in a new installation, the possible extra cost of wiring with radial circuits is small.
