The motor on the back of that bike doesn't look 12" in diameter. If it whines when you push it backwards, but makes no sound when you push it forwards, then it does have internal gears. If it doesn't, gearless hub drives are fairly useless for climbing steep hills. The torque doesn't reach rating until about 100 rpm. The geared ones are useful. The rotor inside runs 5 times faster than the bike wheel. Torque is much higher at low speeds.
All the mid drive mania above glosses over a huge pitfall. Unless the sprocket on the back wheel is bigger than the one inside the mid-drive, it does not have torque multiplication. Only speed multiplication. As you notice, bikes with 48 or 50 tooth rear sprockets cost mid $$$$. Or LLLL in your case. I couldn't even find a 32 tooth 7 speed freewheel to fit my rear hub drive. In the catalog, never in stock. 28 teeth wouldn't get me up the hill when the rain took out my throttle, even with a 32 tooth front sprocket.
What mid drives do better than geared hub drives, is climb 1000' in an hour without overheating and shorting the windings. There is not a 1000' hill in the UK IMHO.
You may be able to use the same frame controller & battery, but buy a power wheel (with the same connectors) that
is geared. I'll wager a Mac12t geared hub motor will climb your hill with a 25 A controller, if you plus bike weighs less than 150 kilos.
https://www.alibaba.com/product-detail/Mac-bldc-hub-motor-6T-8T_60512780782.html I'll not wager that UK customs won't confiscate either at the port or airport. Its still legal to buy these things in the US, but not to ride them on road in about 48 states. Mine had a top speed of ~23 mph on 48 v (54.6 max) but the deadly 750 w limit means its not a bicycle motor under the 3 class system. Domestic retaillers have stopped selling them here. What mine would do is start 150 kg me+bike+groceries up a 15% grade, and accelerate to about 9 mph uphill, without help. Retired bIke riders riding 9 mph uphill: we may as well be displaying Uzis!
