Parking at Paddington

Riding to Paddington from where? There are two bike parks at Paddington - one for anyone and one for those with season tickets. There are also various nearby locations where a low value bike can be chained up, but I'm confused by your ride and then "train" comment as that implies commuting out of London. Otherwise you would be taking a Tube, not a train.

[i]If[/i] riding the extra bit of distance means you have access to more secure parking, then by all means do it. Riding in central London takes a bit of getting used to but with some planning, as mentioned in posts above, it's not as bad as it may first appear. There are lots of side streets and quieter alternatives, and even if they're longer they may be faster.

I usually ride the most direct route in the morning because I want to get to the office as soon as possible, but going home I use an alternative route that adds about 3 km but is virtually traffic-free and has long stretches without traffic lights where I can build up a lot more speed. As a result the longer route usually only takes an extra 3-5 minutes.

The old spray with brown paint trick is a good idea too. It can render a decent bike completely valueless in minutes whilst having no effect on functionality.

The missus has an alloy Giant with thanks to the addition of a mix of brown and red paint looks completely rusty! Its been left in dodgy places with the most flimsy decathlon cheapo lock.

I think the trick is to make sure ALL the components get covered, file off any fancy logos on the components.

If you have a decent new bike, you can guarantee at some stage it will be nicked if you leave it unattended in London.

Mine was only a Specialized that I got 2nd hand but it was under 2 years old. I used to leave at Victoria Station, chained up with 2 d-locks. It was right outside a office with a security guard sitting there in a reception area looking through the glass directly at the bikes. I still can't believe it but someone in broad daylight, in the middle of summer, in a very busy area cut through the locks of the 6 or 7 bikes there and took them all. My theory is they dressed up as an official from the council or something like that. Wankers.

Yep, a 20 mile round trip isn't too much. If you plan your route properly you should be able to skip Tottenham Court Road. It is busy and I can appreciate why you'd want to keep away from it. There are a lot of smaller roads in the vicinity that could get you where you want to go without having to endure heavy traffic. Having commuted in London for years I know that taking backstreets means you avoid the traffic pain and if you work out the route carefully, you can also skip a lot of the signalised junctions that cause so many delays. Try a few trial runs on a few Sundays and you can find a route that'll avoid the pinch points.

If you do plan to park your bike at Paddington I'd advise getting a cheap secondhand clunker. You can get something fairly decent to ride for not too much and not have to worry about it. The charity shop down the road from my work has a secondhand Carrera for just £129 for instance. It's nothing special but it's not some heavyweight boat anchor. Another shop nearby has a secondhand Carrera MTB for £110, which I'm thinking of adding to the family collection as it'd suit my son. Use the cheapo for commuting and keep the shiny bike for weekend rides.

20 mile round trip = 10 miles each way?

For the sake of security I'd ride each way, 10 miles is a manageable distance and can be ridden well under an hour.