EMILY: I am conscious that I may be close to the moment when wearing a bikini in wider company than my back garden is no longer an option. Don’t be ridiculous, says the wonderfully French and un-sticklike Catherine, of Amelie’s Folies in Clapham. You just need to know the type of suit you should buy for your body.

Bandeau bikinis are out for me: not ‘flop-friendly’ in the bosom department. There goes the H&M one I had my eye on. I should avoid underwired tops because I have a pigeon-holed rib cage. Triangle bikini tops are OK because I am less than a C cup (unless you have implants when you can ‘have anything!’) but they should never meet in the middle. Halternecks are excellent and I should overcome my dislike of sweetheart necklines which are almost universally flattering. I should buy bikini tops that have a tie at the back to adjust for stretch over time.

Ample bikini bottoms just emphasise big bottoms and single dark colours have the same effect. A ‘safe’ black bikini is a disaster. Rather I should go for big patterns (fewer repeats), covering a smaller area following the ‘natural line’ at the top of my leg. The 50s’ style boy leg is a hard shape to carry off as it finishes lower on the hip at the widest part of the body. I should aim to cut roughly in half the area of flesh between my tummy button and my pelvis.

We move on to swimming costumes. Ruched panels across the tummy are good. A horizontal seam below the bosoms breaks the expanse of costume and, because I am long in the body, will flatter. Stripes, yes, horizontal stripes are very slimming. I try on the same costume first in blue and white stripes and then in red and look noticeably slimmer in the stripes. Orange is a good colour for me (which I would never have picked out). She makes me try on a cutaway costume a la Liz Hurley. “I couldn’t possibly wear that,” I splutter. “Yes you can.” Amazingly she is right.

She has tips for longevity of swimwear. “Lycra does not like suntan lotion.” Remember to rinse out your costume at the end of each day. Last of all, remember to tie your sarong round your hips – never, never round your waist.

Amelie’s Folies  34 Webb’s Road, SW11 Tel: 7924 5461

A DARK 50S’ BIKINI BOTTOM – dark single colour emphasising the hips are out.

BANDEAU BIKINI TOP – not flop-friendly.

STRIPED COSTUME – stripes are slimming.

A FLORAL COSTUME – large patterned floral repeats are good.