Apparently, you can have any sized bag as a hold bag, as long as it’s under 20kg. But bikes are treated differently. However the wording seems to suggest that they are expecting a complete bike.

Has anyone tried to argue with flybe that a compactly packed bike is simply hold luggage?

Flybe’s rules on bikes are:

Bicycles

We accept the carriage of bicycles on a stand-by basis only. Carriage will thus only take place if there is sufficient space available in the hold and is subject to a fee. To ensure the safe carriage of your bicycle, we require that your bicycle be prepared as follows:

Handlebars must be turned and locked in line with the frame.
Pedals must be removed or turned inwards.
The front wheel must be removed and securely attached to the frame.
The tyres must be fully deflated.
The bicycle must be bagged or boxed, wherever possible

It seems you can take any size hold luggage as long as it’s under 20Kgs as you say.

I don’t see what risk you take just turning up with your sub 20Kgs bag and just checking it in, in fact you take less risk as they only take bike as standby only, so it could be left behind and you don’t seem to be able to pre-book them.

They used to be the best airline for bikes – they flew under BA’s old rules which meant bikes were free! Sadly, it’s not the case any more for Flybe or BA.

I booked a bike with them a year or so back.

Essentially they charged a fee which you paid in advance, it was £25 each way or something like that like most other airlines. They wouldn’t guarantee carriage of the bike. So I had to turn up and hope that they would take it.

In practice it wasn’t a problem but they did emphasise the fact that there’s a fair chance they wouldn’t take it. I’m not sure how much of it a risk it is but certainly added a bit of stress.