Ah, Lit - sounds cosy! With cycling, I was thinking more of maintaining weight and general endurance rather than speed for running. To be any use, it needs to be mixedwith quality run sessions too. That said, lots of fell runners reckkn hard hilly miles kn the bike are excellent for running climbing too.
Andrew - when you add in the biking and swimming it's not as surprising as it first seemed that your running times are so good, and especially XC. I always work on the basis that cycling miles are worth about half running miles, which is roughly the same time wise. Not sure about swimming - in the past I've used it more for recovery and maintaining weight, but was never very serious. It must be good for all over strength though, which is one of the things needed for XC. There are plenty of decent runners who seem to thrive on this sort of variety - Rob Jebb and the Brownlee brothers for a start. It must help with minimising injury too.