Because caught up with Zac Posen for a coffee in Claridge’s. As well as his five-year television success with Project Runway and with a cookbook in the works, Posen’s idea of relaxation is a weekend at the studio to do some quiet, contemplative draping. The designer works on 16 collections a year for his signature line as well as for Brooks Brothers (for which he is creating the ultimate "sisterhood" wardrobe offering practical and empowering solutions to how to dress). His pre-fall collection for Brooks Brothers starts to arrive in the Regent Street store this week – classic pieces reimagined for work and off-duty, made with an experienced eye for the most flattering of cuts and proportions.

Caption: A look from Brooks Brothers' autumn/winter 2016 collection

Why are you in London this week?

I’m doing a dinner for Brooks Brothers and a talk at the Victoria and Albert museum. I’ve never done a lecture there. They were the first museum to have a piece of mine from when I was a student at Central Saint Martins, which looking back was so momentous. I must have been 19 or 20. It was for an exhibition called Curvaceous. I think it’s one of the greatest institutions in the world. I lived and breathed it whilst I was a student at Saint Martins.

What is the first thing you did this morning?

My creative director and partner Christopher, who is French, got up early at 6:30 am to visit his parents in Paris, so I woke up early and checked Instagram. I also check the stock market and global market, as it affects my industry.

How many hours sleep do you need?

I need about six hours sleep –  but do better with eight. I’m a morning person and a night person, I can swap because of the amount of different timezones I travel to.

If power dressing defined the 80s, what is the new definition of workwear?

With workwear, we are definitely living in a moment of personal expression. I have weird feelings about power dressing as I think it’s really associated with ideas of women dressing in things that symbolise ideas of the masculine power with the large shoulders as a silhouette. I’m an obsessive tailor.

We are living in a more casual time. Shoulders are still important but it’s more of a tapered shoulder in, not an extended shoulder out. We are living in a world where flou and structure can play together. There is definitely a sense of mobility today in the fast speed world we are working in.

Is power still important?

There is a level of respect in dressing for others as well as for yourself. I believe in the power of dressing. If you dress the part, it gives you a sense of authority, and it has to come from the strength the clothing gives you.

Do you think we have become too casual in our approach to workwear?

The whole world has gone into such an extreme of casual that I think there is a desire to find great luxury basics that are appropriate for the workplace. That is something I thought was missing in the market, and why working with Brooks Brothers is such an amazing opportunity.

We are looking at a very historic moment, [Hillary Clinton’s selection as the Democratic candidate] whatever your political views are, just as a message globally. I feel very fortunate to be living right now in that moment.

Do you see a difference between the way women in New York dress and groom themselves and the way women in London do?

The UK has its own identity. Every culture has its different influences, and what’s amazing about the UK is you have a sense of a very unique, sophisticated reserve in dress which I appreciate. There is something very understated about it. You also have a history of eccentricity.

Caption: A look from Brooks Brothers' pre-fall 2016 collection

What is the dress code at your studio?

I try to let people express themselves but they have to have a sense of professionalism. I’m not interested in a disheveled, dirty look. It’s not acceptable to me. It’s important when making a luxury product that there is a sense of polish. As I grow, I would love to have a uniform.

What’s your absolute sartorial no-no at work?

Flip-flops. And cut-off jeans.

Flats or heels?

That’s very personal, depending on what height you are, what mood you are in. To me there’s something effortless about a flat, but a lot of women find heels empowering.

Skirts or trousers?

Trousers have a level of mobility.

Is there a woman in business you most admire?

My mother.

What are the qualities you most like in a woman?

Confidence, imagination, ambition and compassion.

Are you good at business?

I was born genetically with a very entrepreneurial spirit. My mother taught me profit margin through selling lemonade as a child. Part of the money I started my company with was money I saved selling lemonade and invested.

What advice would you give to your younger self if you were starting out today?

If I was starting out today, I might have treated it in a way where the pieces on my collection level are one-of-a-kind, collector's pieces – to a level of artistry within that takes it beyond fashion. Maybe even beyond wearability.

How has the industry changed since you started?

The fashion reviewer and the fashion voice is something that I miss because when I started it was the very beginning of online. The importance and role of the reviewer, the fashion insider and the fashion director were very important. When I started, every regional city in the world had people coming to review fashion week. Maybe I’m old-fashioned because I miss that authority and voice. Reviews used to be make or break, and now I don’t think that is the case.

Zac Posen's inaugural collection for Brooks Brothers is now available at Brooks Brothers stores and online.

Interview by Tamsin Blanchard