to ask for the BEST tailor in London...

I totally get wanting someone you can trust with dresses you really love - especially if you want to transform them into something versatile without losing their beauty.
I’d really recommend Angelina Studio. They’re local to Eltham (in Greenwich) so handy for SE London, and they specialise in alterations, cut & sew, and embroidery. They’re really detail-oriented, so perfect for something like your Ganni dresses where you need the finish to be spot on.
I’ve seen them do both delicate fashion pieces and everyday wear, and the quality is consistently excellent. Definitely worth checking them out before travelling further into central London.

Where do you live?
Manuella in west hampstead and to be very good but the price and standard you want I don't know.
It's probably not hard for anyone decent at sewing.
Manuella has done since really complex suit alterations for us very well personally.

I've had a good experience with Richard at Sew & Go in Maida Vale, (3 Clarendon Terrace, W9 1BZ).

He let out some trousers for me with panels that were really invisible and altered a jacket by removing an unflattering integral belt bit, so quite skilled work.

Well, a title edit wouldn't have gone a miss then.

I hope @stressedout1994 found somewhere.

Mark Powell……Soho.

YABU for deliberately misusing AIBU for traffic for something you could have looked up on Google.

Good idea, @QueenOfTheLabyrinth .

Whoever you decide on OP, I’d recommend taking in a cheaper dress / one you don’t mind getting messed up first as a sort of “tester” to see if you’re happy with their work first before risking your dresses.

The fabric shop near me has a printed list of dressmakers and always recommended who would be best for what job. Maybe try a fabric shop and see if they have similar recommendations.

Having said that, I think that changing the dresses to tops and skirts would mean some loss of length somewhere. I'd leave them as dresses.

@Precipice , from the OP, it sounds like a job anyone with a sewing machine and dressmaking skills could do.

Then OP wants 'the best' (read: recommended, trusted by someone with a good experience) alterations service. It's clear what she means.

They're not all the same. I've had alterations places ruin clothes.

Bride and Alter (do other alterations than bridal) Battersea. They have a website.

An extremely talented lady with a sewing room located in SW19. Dafynka something - she is on facebook.

Have used both and very happy

The Gold Needle in Hornsey high street.

I don't think that most answers were snarky. For the task OP had in mind, a tailor wouldn't be the right person.

IME places that do 'alterations and repairs' vary. I've used one once and would not trust one again, but that's me.

For OP's dress, I'd look for a dressmaker with qualification in or a good understanding of pattern cutting.
A bridal dressmaker will probably be able to alter a dress to fit. Women who had their bridal gown altered might know someone.

With a tailoring repair, I'd look for a seamstress with a qualification in tailoring. This is not the same as someone who makes simple dresses as a hobby.

Your best bet is word of mouth recommendation.

My suggestion is try a really good well established Bridal shop. Some may not be interested or might be snowed under as it’s wedding season. But try maybe The Wedding Atelier near Paddington or Mirror Mirror Angel Islington. Obviously they may be too busy to do it but they will know good seamstresses who will be more than capable

OP thanks for asking this question. I also have an item of clothing, in my case a vintage tailored jacket, that needs some careful work and I have been wondering how to find a reliable skilled person to fix it.

all I come up with are endless dry cleaners who say they do alterations, but in practice it’s a person sitting there with a sewing machine ready to replace zips and sew up tears in jeans.
I have googled tailors, thinking that’s what I need . Now I have some specific suggestions for places to try, if I go to London, which I may have to do.

So the snarky comments were completely unnecessary.

i still don’t know how to find “a good dressmaker “. There are a few people advertising near me, but I’ve used at least one of them and she’s useless.

I appreciate you don't want it messing up but it's not a difficult alteration. You need a reasonable alterations company not Savile Row.

Yeah and loads of people decided to be narky arseholes for absolutely no reason whatsoever in answering it. That’s her point.

You asked for the best tailor in London.
You will find them on Saville Row.
They won't be interested in your dress.

You asked the question.

Seconding this one.

Thimble tailoring on Thackery street in Kensington

I recommend The Workshop in Crofton Park

Joe Allen in Islington would be good for this

'Savile Row tailor' has a specific meaning. What you need is a seamstress.
It looks like a fairly simple alteration that a good dressmaker could do for you.