your wasting you time, mcb's for a old wylex fusebox will be expensive, you would be a lot safer with a 17 th edition fusebox with either a rcd x2 / mcb mix or rcbo's for extra protection, rcbo's are a lot better, depending on the age of your old system you may be required to bring you earth bonding up to regs at the same time, 16mm to fuseboard and 10mm to water and gas connection within 600mm of first bend, hope this gives you more information, most companies can fit a whole system for around £300
foot, October 2009