I called Maplins in Cambridge, and they had sold probably their last one to Speculatrix, but the assistant queried regional stock and told me they had some in Stevenage.

Called Stevenage, and was told that if an item goes EOL then you can't buy it on the internet anymore doh.

Anyway called in got my purchase.

I've not tried a (USB) keyboard yet, but my (Kingston) 2Gb thumb drive works OK.

For newbies like me you need to use the commands mentioned earlier in this thread:

To enable host mode:
$ echo host> /sys/devices/platform/musb_hdrc/mode

plug something in with fingers crossed.

I got the 'USB device not Supported' message. File Manager opened and off I went.

To set N800 back to OTG mode, do:
$ echo otg > /sys/devices/platform/musb_hdrc/mode

Cheers!