10 minutes with...Lily Allen and Sarah Owen

Lily Allen looks me up and down. 'I'd probably stick you in a Roxy,' she says, tea length wedding dress tea length wedding dress before deferring to sister Sarah Owen who disagrees: 'I instantly saw her in the Radio City dress dress actually…' And now the half-sisters and founders of vintage clothing label Lucy in Disguise are both staring intently at me as they attempt to solve my sartorial dilemma.

I've just explained that I haven't worn a dress since my Sixth Form prom , favouring preppy shirts over anything more girly, but a friend's upcoming wedding seems the perfect opportunity to find my feminine side, and I need an outfit that doesn't make me feel like Grayson Perry. We're looking through the Lucy in Disguise capsule range of new designs based on vintage favourites. Lily has pulled out the Roxy, a silky, blood-red jumpsuit that looks great on model Mary Charteris at the launch party later that night, but terrifies me.

Lily's reasoning that I try this brazen 1970s ensemble is: 'It's a good compromise as you can cover your legs black evening dresses at casedress. shop popular brands and stores to find wedding dresses on sale, wedding dress preservation discount it's comfy but you'll still look glamorous.' Sarah is unconvinced: 'What about footwear? She'll need some 1970s wedges to pull the Roxy off.' My face drops (I'm more high-tops than high heels), but Lily is quick to reassure me flats would be fine. 'I never really conform to footwear ideals, though,' she admits, most likely referencing her past penchant for wearing Nikes with prom dresses . Sarah, who comes across as the more business-minded of the pair (although Lily's casual talk of 'growth areas' and 'hero products' suggests that Mary Portas' mentoring paid off) shows me the 1940s Radio City dress she has in mind. 'The long classic silk bias-cut is so elegant and the neckline would look great with your short hair.' It's a great dress, but I guess the problem is, I just don't get vintage. Lily and Sarah gasp. 'Vintage clothes have character. You can let your imagination run wild and think about the life that they've had,' says Lily.

This ready-to-wear pre-fall collection is a new departure for the sisters, whose existing shop in Covent Garden stocks only vintage pieces, to buy or hire. 'Hiring from our store is the perfect solution to your wedding dilemma,' Lily enthuses. 'You don't need to commit - just experiment as a one-off.' It's a good point, but I'm willing to invest, red prom dresses 2011 red prom dresses 2011 and finally I find a dress I like from the new range. Fortnum is a 1940s floral-print tea dress with just enough edginess. So that's my wedding outfit sorted - what about Lily's (she's marrying Sam Cooper on 11 June) short wedding dresses ? 'I'm afraid to say it's not from Lucy in Disguise,' she tells me, 'but it is vintage.'

Lucy in Disguise launches in Harvey Nichols on Monday (lucyindisguiselondon.com)