Page Rank changing at night (UK)

[xur82]

This may sound strange, but true.. I can't get my head round it!
I have many .co.uk and .uk.com web sites but for two of them my page rank changes at night. Earthtools.co.uk is generally a 3 in UK daytime with internal pages at 1. At night (late) the home page goes to a 1 with the internal pages dropping to 0. The same goes for Marblefireplaces.uk.com which is a 2 with 1's by day and 0 with 0 at night..
What's that all about? Cheers.