Yes your HW80 will come with a reduced power UK spring. Over here they are rated at 1K fps out of the box, and that is with a standard 8 grain lead pellet. Since the HW80 is being reduced in power it would be easier to restore that power than to bump up the power of a weaker offering.
Pyramid Air ships to GB I believe but they will not ship a part that conflicts with British law. Still, the Vortek kits come with a variety of caps, spacers and washers of various thicknesses so one can reach the proper power level inside that legal limit +- ???
https://www.pyramydair.com/a/Accessories..._Kits/1347
There are also "air gun tuners" that produce kits for rebuilding air rifles there in the UK.
Air Arms offers the Tinbum kits so one might try there although they will certainly offer the 12lb limited kits.
Often the installation of a new tuned kit will be a surprising change since what one thinks they have might not be all the power a legal limit kit will provide, along with the smoother operation of custom parts inside.
I do know some folks find industrial spring makers that have extensive offerings of industrial springs which will match the diameter and strength of most standard air gun springs and they can be ordered in random length. Find one with a couple of coils more than your present spring and keep it as a backup.
And one can always bump up their stock spring. That is usually done by adding a plastic spacer either around the piston guide at the front of the spring, or at the base of the spring where it butts against the rear of the tube. I have seen 50-75 fps gained with spacers.
The spacer against the base of the tube sometimes causes cocking problems but the nylon washer in the piston tube is usually not a problem. Those Vortek kits come with a variety of those spacers and washers.
At any rate when you bump a spring to higher power and approach that 1000 fps mark you must go for a balance of power rather than raw speed. You increase your power level by going to a heavier pellet at less than 1000 fps. With a more powerful rifle you move to a heavier pellet and keep it just below the sound barrier to maintain accuracy and stability of the pellet.
A flatter trajectory is not the goal at that point, because of the loss of accuracy due to instability of the pellet.
So you find yourself trying to hit that "sweet spot" where one has more than "standard power" but not passing the 1K fps stability threshold. A 10, 11, 12 or even a 15 grain .177 pellet may be needed.
If you try to hit that spot you only have about 150-175 fps to play with by mixing and matching pellet weight to speed. You will hear all kinds of screaming on the forums about newbies that installed a stronger spring and it ruined their accuracy. They have simply worked for speed rather than moving away from the discount store pellets and working for the best balance in their rifles.
With my PCP rifles I have moved to 16, 18, and 20 grain pellets and maintain a speed of about 900-950 fps. A springer that will do that does considerable bouncing and hopping about in its effort to shake itself to death. It will also kill a scope in short order. I have one 1k springer that stings my face due to vibration every time I pull the trigger. It is not pleasant at all!
And with an increase in power level there is that increase in self destruction potential, as well as increased cocking effort. 50-60 lb cocking effort is now common and most of the rifles with "moderators" are not really moderating anything they are offering a longer barrel with a great big handle to help overcome the tremendous spring inside the rifle.