Practically any scope can be used for HFT - something around 8-10 mag will work best.
To illustrate a point - I've witnessed UKAHFT national events won by scopes that most people (including me) would say aren't really a suitable scope for HFT. As an example back in 2006 I think - Andy Calpin won the UKA event at Lincs using an FT scope - Tasco Customshop 10-60x60 with high mounts and an ordinary ret I think. He shot on 10x mag but high mounts and 60mm objective lenses is something most people would advise against.
I've also witnessed someone clearing a UKA national course with a 20x mag scope.
The point being - it's down to the shooter, not the scope.
If you're new to HFT - my suggestion would be use whatever you've got - try to set the parallax to around 25 yards and your mag to around 9x-10x if you can to give you the best chance.
Instead of buying a scope and spending time setting it up, invest that time into accurately recording and learning your holdovers. Use some of the money you've saved by not buying a scope to buy pellets and spend time perfecting your technique - trigger, breathing, follow-through.
Once you've shot your first HFT comp, look back on it and try to figure out the main reason for dropping points - and work on fixing those things first.
From my experience the most common reason for dropping points when you first start is not having a gun that's been set up, followed by not knowing your holdovers, followed by poor technique. Sorting those things out will gain you more points than buying a new scope - I guarantee it.
If I were you, I'd take Chris up on his offer - not only is he an excellent shot, he's also a top bloke who will go out of his way to help you out. He might even give you some tips on setting your gun up.
Also have a read of the Novice to Ninja articles - www.anstonftc.co.uk/novice-to-ninja