Bikes on trains in London

each operator has different restrictions, and even on the same train there can be different restrictions depending upon origin and destination. And there are oh so many operators and brands of operators in London. By terminal:

Fenchurch Street

 - c2c

Liverpool Street

 - Greater Anglia

 - Stansted Express

 - TfL Rail (pre-Crossrail)

 - Overground

 - (c2c at weekends)

Kings Cross

 - Great Northern

 - Virgin Trains East Coast

 - Hull Trains

 - Grand Central

St Pancras

 - Thameslink

 - East Midland Trains

 - Southeastern

 - Eurostar

Euston

 - London Midland

 - Virgin Trains

 - (Overground)

 - Caledonian Sleeper

Marylebone

 - Chiltern

Paddington

 - Great Western (very different restrictions on local and High Speed/Sleeper services)

 - Heathrow Express

 - Heathrow Connect

 - (Chiltern once a day)

Victoria

 - Southern

 - Gatwick Express

 - (Southeastern)

Charing Cross

 - (Southeastern)

Waterloo

 - SouthWest Trains

 Cannon Street

 - (Southeast)

London Bridge

 - (Southern)

 - (Southeast)

 - (Thameslink)

Other:

London Underground (Subsurface lines)

London Underground (Deep tube lines)

DLR

(Overground)

Tramlink

For just Thameslink and Great Northern, this is the guide to restrictions. Simple, yes? 

The Overground is good - bikes seem fine much of the time.

   Always be nice to the guard, smile, good morning/afternoon/evening.  Talk to them, you might be alowed on this one...

   If they say no, accept with good grace and try the next one.  Same as if it's too busy and you really shouldn't.

   Sometimes it was too busy on my FGW Reading to North Camp, on which the bicycle was permitted. Would be nice and ask the guard if I could get on the SWT to Wokingham, on which I was not allowed, and they never said no (always very empty, huge train).  I'd have to wait 20 minutes at Wokingham, then the next FGW would show up, crowded, half would get  out, and I'd get on to North Camp, or Farnborough North.  Sorted.

   It can even work on the big trains, though local stoppers are easier,  politeness and pleasantness can get you far, especially if kind of genuine.

was my understand bi-cycles had to be folded but as long as they are thats fine any time of the day - its the case on the tube.

between 6 and 7 pm, then yes i believe you'll be fine heading TO Waterloo, but not FROM Waterloo.

In practise, it depends on the train, I often used to have people getting on at Clapham on London bound trains in the morning rush hour with non-folders and no-one stopped them. 

The whole bike on trains thing is incredibly confusing, with different traincos having different rules. 

Generally, I think you aren't allowed bikes on trains due into or out of Waterloo in the rush hour.

The trains are very busy at those times and people will be struggling to get on in general. Even if they were technically allowed I still wouldn't.

"Bicycles cannot join or leave trains bound for London Waterloo, Reading, Hook, Alton, Guildford and Dorking, due to arrive at London Waterloo between 07:15 and 10:00 inclusive and between 16:45 - 19:00." www.southwesttrains.co.uk/travelling-with-us/cycle-policy--schemes

You could try the "it's not a bike, it's luggage" angle - might work better if could you wrap/bag it?