Can't rely on me today cos my iPad charger was shit and I had to find another one but fortunately the cavalry arrived
To chuck in a couple of answers to queries up thread and bore the pants off of some of you.
Wearing an ill fitting bra constantly can cause breast tissue to reshape in the same way that badly fitting shoes affect the shape of your feet. It's especially common amongst middle aged/older women, and those from overseas, in both cases due to lack of previous size availability. The UK is now regarded as the best place to come to for good bras, which considering how many people have had poor fittings on these threads, is quite worrying!
Additionally, if your breasts are naturally wide or wide spaced, it's less obvious that your bra is too small as you're not always falling out of the centre of the bra. Constant squashing into a too small cup can create a pouch of breast tissue under the arms, which remains obviously 'separated' even once the bra is taken off. Since starting the interventions, we've heard many anecdotes of being able to massage the tissue back into the main breast by regular scooping.
The other issue that creates bulges in a correct size is that the bra cup is not wide enough for the individual breast. This can cause the armpit overflow described above, and scooping won't fix it- a different bra style is the answer.
Ive noted over many years of bra fitting, that rib shape can majorly affect the fit and comfort of a bra. My own ribs are quite flat and wide, so although I only measure a 30 band these days, a bra with the wrong shape wire will still feel too tight in a 32 or even a 34.
I've taken to likening wire shapes to smiles 
If you have breasts sited lower on you ribs and closer together, then your breasts are more likely to project forward and brands like Panache may feel right, as their wires are in quite a deep U shape.
Higher rooted, more spread across breasts tend to need a wider 'smile'- the wire will wrap more around the back rather than pointing up into the armpit.
Freya half cups are a particularly good example of this.
Of course there are many variants, even within those two brands and what is great for one woman, will be agony for another.
All I can honestly say is don't rush when choosing a bra, you may have to try on dozens to find the right one for you, but when you realise that you have forgotten you're wearing it apart from the compliments you're getting from your friends about your figure, it's so worth it