OK. 100 pounds is like 169$ US. For that money, the Alesis micro gate ( i forget the name exactly) is a 1/2 rack two channel gate. I had one for a long time and it worked very well. I had no complaints at all. For the same $$$ (sub $200 US) the Samson gate/compressor/expander is what I run now. A great unit also.
I second the Alesis Microgate. I've used these in my studio for over ten years. I haven't purchased anything newer because the Alesis gate works so well. It’s a true stereo gate and has great specs.
They are no longer in the current Alesis product line, so you will have to find one used. Expect to pay no more than £50 on ebay UK.
Here is the manual from Alesis if you want to check it out: