Panniers as Carry on Luggage (British Airways)

I'm soon to be going on tour where I'll be flying out of Heathrow (T3) with British Airways.

For the tour I will packing relatively light and will just be taking my two Ortlieb Back Roller Plus panniers (20l each)

I have 1 piece of checked luggage booked which will be my bike with rear pannier rack. I'm planning on strapping my tent poles to the top tubes. Am also trying to think of ways that i could affix other pieces of luggage to it without a pannier rack, hopefully reducing size of panniers.

Has anyone got any experience of taking panniers (potentially pretty pretty rammed) as hand luggage. My experience with my in the past has made me think that they're a little more 'flexible' with the boundaries of their hand luggage allowances as long as you're not taking the piss.

At this stage they're quoting £96 to add another checked bag to the booking. This would probably have been only £40 at the time of initial booking so I feel like a bit of a muppet already.

panniers are fine. you can squash them down easily. when I flew BA I put all my heaviest shit in my carry on panniers, that way the bike (cardboard) box wasn't overweight but contained the bulkiest stuff I didn't want to carry on (eg. sleeping bag)

when i went a couple of years ago, i put the bike in a box as normal

with my panniers i loosely packed them, put them top to tail and stuck them in a thick plastic bag which i taped up.

i then took this as carry on, got some funny looks but no issues.

My approach has varied from taking a Sainsbury's bag for life, putting all my luggage into it and taking that on board, to (most recently) buying a folding "holdall" from Ikea (£4) and dumping the stuff into that. Both times the bag fitted into the allocated space frame thingy at check in with room to spare.
This is the Ikea bag, although mine is black: https://www.ikea.com/gb/en/products/ikea-family-products/travel/knalla-sport-bag-black-white-art-50330507/

Nice one - just to update this thread, none of the staff at either Gatwick or Malaga gave two shits about two solidly full 20L Back Roller Classics and a helmet.