Earlier UK regulations required that the motor has an average power output limited to 200 W (250 W for tricycles and tandems) and weight limited to 40 kg (60 kg for tricycles and tandems). These regulations must come in-line with the EU regulations by (find deadline). For models sold before June 2003, e-bikes conforming to the speed, weight and power limits may also be considered pedal cycles. Electric bikes with higher power outputs, or those not meeting the "pedelec" definition are now treated as motorcycles and require a license.
I converted my Kona Dew Deluxe to electric with a controller and 1000 watt front wheel. The SLA batteries I tried initially were _functional_, but the bike had a range of about 6 miles @ approx. 50% throttle use. Since upgrading to the Joyisi pack, the utility of the bike has increased exponentially. I need to add a better gauge so I can drain the battery more fully between charges, but I'm getting at least 20 miles per charge, including some very aggressive uphill segments. On flat ground, the battery powers the bike to approx. 35MPH; even on really steep hills with minimal pedal assist, I do at least 15MPH. Biking 15MPH uphill with little/no effort is EPIC.
And let’s not forget the economic advantages of owning an e-bike. The annual cost of running a new family car is, on average, about $9,000 per year. Running an electric bike costs around $400 per year. And while filling a gas tank costs around $30, recharging an electric bike battery costs only about 50 cents. A tank of gas may get you further, but not 60 times further!