Where to go for a spa day in London

For a long soak, AIRE Ancient Baths near Covent Garden is the place, and it stays open late. For a treatment with a swim afterwards, go to one of the Mayfair hotel spas, where booking a treatment is usually how you get in.

AIRE Ancient Baths, off the Strand

AIRE is in J.M. Barrie's old house on Robert Street, a short walk from Covent Garden and Embankment. You work your way round a circuit of baths at different temperatures, and you can book the baths on their own, add a massage or go as a pair.

The hours are the reason to go: 8am to 10pm Monday to Thursday, 9am to 11pm on Friday and 8am to 11pm at weekends. A late session after dinner in Covent Garden is about the best way to finish a long London day. Weekend evenings sell out first, so book the moment you have dates, and bring swimwear. Couples do better on a weeknight than a Saturday, when it's fuller and the baths get louder.

The hotel spas in Mayfair and Knightsbridge

The Connaught's Aman Spa is small, dark and calm, with five treatment rooms, a pool, an aromatic steam room, a relaxation lounge and a private gym tucked deep inside the hotel. Non-residents get in by booking a treatment. A 75-minute facial on the current menu is £275 and comes with two hours of spa access beforehand, which is the right way to do it: arrive early, swim, steam, then go in. For two, the Gong Fu Cha tea ceremony is an unusual alternative to a massage at £320 each for 90 minutes, with a minimum of two guests.

A few minutes' walk away, Claridge's Spa has seven treatment rooms with their own bathrooms, a relaxation pool designed by André Fu, steam rooms and saunas. It's open daily from 8am to 9pm, but the first two hours are family swimming, so book an adult treatment after 10am if you want the pool to yourselves. Regulars come for the resident specialists: facialist Teresa Tarmey, colourist Josh Wood and the skincare brand Augustinus Bader all work from here. The spa's own pages are vague on non-resident bookings, so ask when you call.

Surrenne Belgravia is a members' wellbeing club over four floors of The Berkeley in Knightsbridge, with a 22m lap pool, seven treatment rooms, a Tracy Anderson studio, steam rooms and a hyperbaric chamber. Hotel guests get membership thrown in, but for everyone else it's a club rather than a drop-in day spa, which suits a long stay better than a single afternoon. Ask the club directly about membership or day access.

Porchester Spa, and booking well

At the other end of the price scale is the Porchester Spa, a set of historic Turkish baths in Bayswater that reopened after a multi-million-pound refurbishment. It's the place for a plain heat-and-plunge session without hotel prices, and it suits a long-stay guest in Bayswater or Notting Hill who wants a regular sauna habit rather than one big afternoon. Check its website for the current women-only, men-only and mixed sessions before you go.

The four central spas are all a short taxi ride apart. From a Mayfair base you can walk to Claridge's or The Connaught, and AIRE is two minutes from Embankment on the Bakerloo, Circle, District and Northern lines.

Saturdays go first everywhere, so book two to four weeks ahead; a weekday morning gets you the calmest pool and the widest pick of therapists. Before booking, ask:

• Does the treatment include the pool, steam room and sauna, and for how long before and after
• Are non-residents welcome, and is there a minimum spend
• Is there a family swimming window when children use the pool
• What the cancellation notice is (often 24 to 48 hours)
• Whether robes, slippers and swimwear are provided