DVSA: Driver and Vehicle Standards Agency
MSVA: Motorcycle Single Vehicle Approval scheme/test.
Do the bikes conform to the EU’s EN15194 regulations?
The basic stipulations of these are:
The bike must be pedal assist, not throttle-based
The bike must have a continually rated power output of 250W or less
The speed limit for assistance must be 25km/h
If they don't, and you put it through the MSVA in the UK it gets classified as a moped.
"Anything faster or more powerful than the EN15194 regulations allow technically needs to be type approved as a motor vehicle. There are two standards: L1e-A, for motors up to 1Kw and speeds up to 25km/h, and L1e-B, for motors up to 4Kw and speeds up to 45km/h."
If it doesn't meet the EN15194 regulations,
"There's a lot of paper to wade through
First, find yourself a bike. You’ll need to make sure it comes with a Certificate of Conformity, and that it conforms to 168/2013/EU regulations; you’ll need the certificate later.
Head off to the DVLA and get yourself some forms. You’ll need a V267 (New vehicle import pack) and a V55/4 (Application for a licence for a new motor vehicle and declaration for registration). They take about a week to arrive.
Complete the V267 & V55/4 with the information from the Certificate of Conformity.
Send everything with a cheque for £55 and the original Certificate of Conformity off to the DVLA. You’ll need to include a bank statement and/or utility bill, and a copy of your driving license or passport.
Wait for your V5C registration document to come back: this takes about two weeks
Check your vehicle tax - it’s exempt, so there’s nothing to pay
Get a standard vehicle number plate (around £10 online) and fix it to the rear of your bike
Arrange some insurance - Bikesure quoted £135 third party only & Quoterack quoted £200 fully comprehensive for this bike
Find yourself a kite-marked motorcycle helmet. An open-face moped helmet will cost from about £30 upwards.
And you’re done! So you’re looking at a process that’s likely to take about a month, and cost you at least £200, on top of what you’ve spent on your bike."
The above, in italics, is Riese und Muller bikes UK response to the regulations as they apply in the UK*. S-pedelecs/speed pedelecs aren't recognised in the UK.
As for your suggesting "you need to put a 250W rating sticker on it", its illegal. In the EU and UK. The placement of that sticker is covered by/in the regulations.
And yet you're telling someone to do it.
*
https://ebiketips.road.cc/content/advice/advice/buying-and-riding-an-s-pedelec-in-the-uk-1637