Whenever there is the slightest bit of rain BBC/2 etc all go AWOL with 'bad or no signal'

All channels are fine.

I have just been watching BBC Interactive fine - then when I extited that to return to BBC1 I got the 'no signal' message.

Is it normal to get most channels fine and some not at all?

On a side note the Humax 'locked up' yesterday and would only come back to life with a power off/on - this resulted in lots of progammes being lost / duplicated (but not playing). from reading around this is just a 'known' (but unaddressed) bug with Humax - but thought I would mention in case it had any bearing on not recieving BBC2.

A)Do you have other copies of those channels numbered 800, 801 etc ?

B)Is your signal strength/ signal quality much lower on the affected channels than those which rarely/never suffer ?

If A you need to manually tune the channel frequencies for your preferred transmitter.

If B, but not A, you need to determine whether your aerial is suitable for the frequency that the affected BBC channels are broadcast on (may need a wideband aerial or a different group, to receive all the digital channels), or whether the coax cables (particularly those immediately before the PVR) are substandard or damaged - if they are like washing line they should be replaced with thicker ones made from similar coax to the aerial downlead.
Also if you have any equipment with a modulator (VCR, Sky), or HDMI (console, DVD, SkyHD) outputs try turning those off to see if that resolves it.