Wow this thread has really kicked off! Finally read to the end 
Thanks for all responses and support. I feel a lot more confident about feeding my baby in public now. It's also good to know the people who object to public BF are in the minority. I will continue to BF wherever and whenever DS needs to be fed!
I had a chat with DH, who said he is very pro-BF and finds it beautiful, but he doesn't like other men to see! Which explains why he often stands up and tries to shield us with his body/block other people's view when we're in public! Having said that, my mum does the same although for different reasons... she thinks it's 'daring' to feed where people might see... when I fed DS in the back of a taxi she kept trying to hold her coat up like a shield, presumably in case the taxi-driver glanced in his mirror and caught a glimpse of my boob 
To the posters saying do it discreetly, I would if I could but it's difficult. I've tried the 2-top method but the top layer slips down onto DS's face and makes him pull back. I've also tried nursing-tops with holes, but struggle to get my bra unclipped and my nipple through the hole when DS is screaming and thrashing (he's very impatient when hungry). So I tend to wear wrap-dresses or low-cut tops that I can just pull down at one side. Which means yes I do need to get whole boob out, as DS struggles to latch and I need to hold my boob with one hand, support his neck with other and sort of shove boob into his mouth until he latches properly. I usually continue to hold boob while he feeds as he slips off easily (mild tongue-tie midwife said didn't need treatment). So I don't see how I can avoid getting the whole boob out and there's a good chance people may see a flash of nipple during the struggle to get him latched. Oh and to the poster who assumed I had 'big floppy breasts'
I actually have B-cup breasts (that expand to a DD when full of milk). And no I don't 'wave them around'
. The reason I was in the 'middle of Costa' was not me trying to make a performance out of BF, but the only place there were free tables with space for pram.
I often feed in front of close friends and would be mortified if I thought they found it embarrassing or offensive. They don't seem to mind at all and are very supportive, getting me drinks if we're out, passing DS to me etc. They seem to find BF natural and normal.
Re expressing milk, I do this anyway so DH can do some of night feeds, but I prefer not to carry a bottle when out as would also have to carry breast-pump and find somewhere to express to prevent engorgement (had mastitis at start, don't want that again!) Also I prefer BF as it's correct temp for DS and less hassle than carrying bottles.
I'm curious as to why people who dislike seeing BF mums can't simply look the other way?