Would also echo someone's comments above - from SE22 to the city, almost no difference in commute time between a motorbike and a bicycle. I do find the moto much more pleasant through winter though.
Mid-way compromise is a power-assist pedal bike. Means you can ride a heavier and more comfortable bike with full mudguards for the winter, without being a slog to haul it over distances.
- Good for the environment and your fitness - the level of exertion is about equivalent to walking, but you go 5x as fast.
- Quiet (unlike petrol engined scooters)
- Great safety record
- Inexpensive to run - no insurance etc.
- No compulsory training
- No need to fill up on fuel, ever - charge the battery pack at home or work from normal mains socket
- Can bring it home on the train (and the "surface" Tube lines, overground etc.) if it's late and rainy and you've had a few drinks
- Power assist means you can run with full mudguards, panniers and waterproof gear and not get sweaty or wet
- Can use all the cut-throughs, cycle lanes, cycle early starts, parks, paths etc. which are closed to scooters
- High initial purchase price for a good spec model, £1000 is the minimum for something that will last although prices are coming down all the time
- Relatively low top speed, the power assist cuts out at 15mph, as such it's much less comfortable than a 125 if you need to mix with traffic on a 30mph road
- Maybe not as comfortable as a scooter
- Can be heavy, but for security reasons (see above, high purchase price) you want to store it indoors or in a bike shed. This can be a problem if you need to take it home via a station that doesn't have lifts, or if your workplace has no arrangements for bike storage.