Although I'm not up to date with UK duties: In general computer equipment is exempt from duty. Check with your local customs office to be sure. Also make sure to tell the clerk you order from to properly identify the equipment in the waybill: I got stung for $20 CDN in import duties because an RFX9600 was improperly identified as an amplifier (go figure!). It is a networking device by nature and construction!!

I'd be very happy to save 70 to 100 pounds! That's 140 to 200 Canadian Dollars which would keep me in beer for a couple of months!

Regarding warranty: Yes you've gone and bought an item from another country and yes your warranty would be less than valid. Thus if warranty is a concern or if you are nervous about buying on-line: Don't! But the RFX is all solid state circuitry and its not made in China! Unless the shipping box gets whacked to death; the unit should be fine.
Also check the sellers return policy: B&H are very good about dealing with / addressing anything DOA (Dead on Arrival) or BOA (Beaten to Death by Fedex on Arrival).