I know a fair bit about e-bikes.
Don't try making your own - you could buy one for less.
Anything less than £1000 or so and the battery capacity will be compromised - and 62 miles is a fair old distance. There are plenty of cheaper bikes out there but you won't be seeing them at my bike shop - at least not for sale. Had a few on the stand and not been impressed.
Focus do some really good ones. As do Kalkhoff. Both are using the Panasonic drive system which sits in the BB area and balances the bike better. But I suspect neither are available in the UK.
Personally - avoid "rack" type batteries and front hub drives.
Completed: 94 Stumpjumper w. M733; ; 92 Dave Yates 731 ; 97 Parkpre Pro-Elite ; Pace RC200 F6 ; Pace RC300; 82 Gios Super Record ; 97-8 De Rosa Giro D´Italia; ; Banani SPX Track bike ; 89 Alan/Mavic Cross Bike ; 05 Focus Cross Team ; 90 Look MI-80 all-Mavic ; 12 Focus Izalco Team/custom build ; 11 Focus Thunder Custom build
Projects : , Brouwer all-Mavic
Stripped : Pace RC303
Gone : GT Karakoram
Stayed in the family: Kuota Kharma, 04 Stumpjumper FSR
Ceased to be : Dynatech MT3, killed by corroded seatstays.