Sur-Ron and the wave of similar electric dirt bikes that followed it have genuinely changed who's out riding off-road, light, quiet, and a fraction of the running cost of a petrol trail bike. Whether one's legal on a green lane depends entirely on which version you've actually got, and the honest answer is that most of the ones on the road right now aren't.
The bike matters more than the brand
A BOAT is legally a public road, the same as we've covered in do you need tax, MOT and insurance to ride a legal green lane, and that means the vehicle using it needs to be road-legal, full stop, whatever powers it. The standard off-road Sur-Ron Light Bee and the Ultra Bee dirt bike are sold specifically as off-road machines, with no type approval for road use at all. Bolting on a numberplate, a horn and some indicators doesn't change that, they were never designed or certified to the standard the law actually requires, and there's no legitimate route to making one road-legal after the fact.
Sur-Ron does sell genuinely road-legal variants built for exactly this, the Light Bee L1 (registered as an L1e moped) and the Ultra Bee T (an L3e motorcycle), both carrying real EU/EEC type approval alongside the lights, mirrors, horn and speedometer a road vehicle needs. Bought through an official dealer, DVLA registration is normally handled as part of the sale. The moped-class version also needs the same Compulsory Basic Training any 125cc-equivalent rider needs before riding on the road, a BOAT included.
So can you actually ride one on a green lane
Only the properly type-approved, registered version, and only once it's taxed and insured like any other road vehicle. An off-road-only Sur-Ron on a BOAT is in exactly the same legal position as riding an unregistered dirt bike on the road outside your house, it doesn't matter that the terrain looks similar to what the bike was actually built for, the legal status of the ground you're on is what counts. Riding an unregistered, untaxed, uninsured vehicle on a public highway carries real consequences, including seizure, this isn't a grey area worth testing.
What about bridleways
Worth heading off directly, since it comes up: bridleways allow walkers, cyclists, horse riders and pedal cycles with electric assistance that meets the UK's EAPC rules, pedal-assist only, capped at 250W continuous power, assistance cutting out at 15.5mph. A Sur-Ron, throttle-controlled and nowhere near that power limit, doesn't meet that definition regardless of what it looks like. A bridleway is off the table for one entirely, road-legal variant included, exactly as it would be for a petrol dirt bike.
The practical takeaway
If you're buying specifically to green lane, the road-legal L1e or L3e variants are the only ones that actually get you there legally, bought through an official dealer with the registration paperwork done properly, taxed, insured, and ridden on the licence that variant actually requires. An off-road-only model is a genuinely capable machine for private land and dedicated off-road centres, just not for a BOAT, no matter how it's dressed up.
Check what's legally rideable near you, browsing the map and checking a lane's legal status is free, no account needed.