Ship shape: Royal Caribbean's Quantum of the Seas

One has a viewing pod on a giant arm rotating 300ft above the sea. The other has a 308ft-long Union flag painted on its bow.

Two distinctive new rivals for bookings from British holidaymakers – Anthem of the Seas from Royal Caribbean and P&O's Britannia – are under construction and both will be sailing from Southampton to Europe from next spring.

At the weekend, Anthem's identical twin sister, Quantum of the Seas, sailed from Southampton to New York, where she will spend her maiden season on Caribbean cruises in November, before relocating to Shanghai next year to capitalise on the lucrative, booming Chinese tourist market.

Richard Fain, the American chairman of Royal Caribbean, has been widely quoted in the travel trade press as saying: "It is my objective to crush our competition in the ex-UK market with Anthem." P&O's marketing director, Christopher Edgington, retorted that Britannia would not rely on "gimmicks," just deliver "the most contemporary and refined holiday experience".

Britannia, specifically for British holidaymakers, focuses on providing the seaborne equivalent of a five-star hotel holiday with "Food Heroes" – celebrity TV chefs, such as Marco Pierre White with his own restaurant, and James Martin presiding over the onboard cookery school. And the spa will have a luxury villa within it offering pampering days for private groups.

Anthem, for the international market, is big on techno-wizardry. Cocktails mixed by robots are ordered on touch screens and paid for by scanning the wristband that opens your cabin door. Inside cabins have virtual balconies – floor-to-ceiling screens that show the view outside in real time.

Simulated sky-diving, a daytime dodgems arena that turns into a roller disco at night, and the London Eye-inspired North Star pod, which takes 15-minute flights over the ship and sea, are some of the unique features. No-fly cruises for the British market are about to take off in a big way.

* A 14-night no-fly cruise to the Mediterranean aboard Britannia, departing Southampton 13 June 2015, includes calls at Vigo, Alicante, Barcelona, Monte Carlo, Genoa, and Gibraltar. Fares are from £1,619pp with P&O (0843 373 0111;

* Anthem of the Seas sails round-trip from Southampton to Spain and France. A seven-night cruise, departing on 7 June 2015, costs from £1,029pp sharing an interior state room, when booked through Royal Caribbean (0844 493 3033;