Primark certainly used to do the backless bras and I know they sell tit tape. If that fails, Boots do tit tape and somewhere like debenhams or m&s will most certainly have some kind of suitable bra solution
Unless they're made of silicone I really wouldn't recommend going bra-less as a 32F no matter how perky you think they are especially if its a cheapish fabric. I'm a perky-ish 32e and know I'd be bouncing about all over the joint plus would be worried about my nipples showing through dress
Are you sure you can't wear a black bra if you got tit tape?
Don't bother with those sticky on cup things - they don't really work for those big of cup and hurt like hell when you try and take them off
Ultimo do backless and strapless but they aren't cheap. You can get low back converters more reasonably which you add on to your normal bra so it hooks around your waist and not around your back. Failing that I'd try those nipple cover 'pasties' to prevent nipping out!