You are right about the link with Halfords. That one looks like a 1990 bike.
As far as I can tell the Eiger was virtually identical to the Tufftrax from the same year albiet in blue rather than magenta.
They both had a 400LX groupset.
The one you have appears to have had the crankset replaced at some point as it would've originally had a limited edition black version fitted.
You appear to have the original wheels and Tioga FJN tyres.
Nice to see it still has the original colour matched reflectors fitted too.
It is a nicely put together bike and the polyester powdercoat should stay looking great for another 20 years.
I have a 1989 Tufftrax which is almost built up to catalogue spec. It looks very similar and it's one that I will be hanging on to.
I've also got 1990 Eiger frameset and 1990 Tufftrax frameset too.
1990 catalogue is here for reference: --> http://www.retrobike.co.uk/gallery2/v/M ... 0.pdf.html