I'm not very good at giving good suggestions but I thought I'd give it a shot
I know it gets cold in London (though I'm not sure if it is currently) so if you had a longish coat that you could wear that would hide you wearing handcuffs, you could go for a little stroll while wearing those. Might be a bit hard to pull off though
Nipple clamps under clothes for as long as you are able to wear them in public. You could tie body harnesses under your clothes also. You stated that anal falls under dislikes and likes so I'm not sure how comfortable you would be plugging yourself in public. If you have a small plug that you wouldn't mind using for around an hour you could go have coffee or lunch while plugged
For petplay, there's not much that comes to mind aside from the basics, but you could both be the others pet for a set time. Spend the day on all fours and doing as the owner pleases I'm not sure if eating out of bowls on the floor breaks the food limit thingy so maybe you could take breaks when it's time to eat. Alternatively, the pet could be hand fed which adds a touch of humiliation
You could set up a bondage session where the bottom is bound to the bed, gagged and blindfolded (you could also add earphones and music for more sensory deprivation) while they are tied, the one on top can use the crops for some light/hard spanks, wax play, edging, forced orgasms whatever it is you want to do
there are plenty of options once in this position!
That's all I've got, sorry most of them aren't great and are pretty basic. Hopefully you two can build on these ideas when more people comment
Have fun
