It is the travel equivalent of shopping at M&S but not wanting anyone to see the label. This summer, thousands of holidaymakers are having to come to terms with an uncomfortable truth.

They would not dream of booking with a mass-market package tour operator, but suddenly that cosy little company whose staff knew their destinations so intimately and made them feel so special has been swallowed by Thomson or Airtours. Can they ever breathe its name safely again across the dinner table?

Since the Monopolies & Mergers Commission decided, more than a year ago, that the major operators did not represent a fundamental threat to competition, they have indulged in an orgy of takeovers. Among those snapped up is Simply Travel, a firm priding itself on quality villas or serviced accommodation in places away from the mainstream. The group carried around 43,000 customers a year. Now it is part of Thomson, which averages almost twice that number in a single week.

Thomson has also bought Cheshire-based Headwater (which offers walking and cycling holidays, carrying customers' luggage between small hotels in areas such as the Jura and the hills of Umbria); Spanish Harbour Holidays (which concentrated on Catalonia); and the Magic Group (whose brochures appear under labels including The Magic of Italy).

Airtours, second largest of the giants, has taken over Panorama, best known for its Tunisian and ski programmes; and two city breaks specialists, Cresta and Bridge Travel, whose brands include Paris Travel Service. First Choice, itself battling against a hostile takeover bid by Airtours, has acquired long-haul tour operator Hayes & Jarvis and ski firm Flexiski.

What difference does it make? Will customers even notice? Thomson argues that it is vital they should not. If long-time customers of its new stable of companies are switched from scheduled flights to charters or if personal service gives way to engaged telephones and staff who don't know their Assisi from their Elba, they will soon vote with their feet. They may pay more for a break at the same hotel than they would with the parent tour operator, but Thomson says price differentials exist precisely because of such differences in service: a taxi from the airport to the hotel, for example, rather than a coach that makes several stops.

The Association of Independent Tour Operators is concerned, however, that it may not exactly leap out at customers from the brochure that their favourite small operator has been taken over. 'The trouble is that con sumers don't perceive any change. But while this year the holidays may be very close to the original, we think there will be big changes in future.'

Among AITO's sceptical members is Noel Josephides, managing director of Sunvil, which has spread its wings from Cyprus and Greece to destinations including Lebanon and Namibia. He believes small firms acquired by major operators will change as the people who built them up disappear from the scene.

'It will be perhaps two years before we begin to see the effects,' he says. 'Will the personal rapport between these companies and their suppliers such as hoteliers survive? New managers coming in may not understand Greeks or speak the language, for example. Will they pay the same attention to detail? Will they push a holiday programme forward with the same enthusiasm if they haven't created it themselves?'

He also worries that small companies remaining independent may face unfair com petition which could erode consumer choice. Operators under the wing of larger outfits will be able to cut costs by getting cheaper bonds - compulsory financial guarantees that customers will not be left stranded or out of pocket when firms go bust. And, because the major operators also own charter airlines, their new subsidiaries may benefit from flights at more convenient times or even the exclusive supply of seats.

'I can handle competition on a level playing field,' says Josephides. 'My worry is that one of my competitors will get seats when I can't'

This would prove doubly frustrating for small firms if it turned out that some villa or ski chalet owners preferred to deal with them than with the large operators but they were denied the capacity to carry the extra business. One result of takeover fever may be a shift away from conventional beach holidays. Thomson has reflected the desire of customers to do more than just flop in the sun with what it calls 'mass customisation' - an attempt to satisfy a greater variety of demands from the same basic assembly line.

As tour firms garner information about customers through increasingly sophisticated databases, they will be able to home in on those clients' preferences - through direct mail or via the Internet.

Suppose a couple on a Spanish sun-and-sand package takes several mountain-biking excursions. Soon afterwards, they receive a message from the operator saying one of its subsidiaries specialises in such trips - and offering them an entire cycling holiday - at an introductory discount.

So, when your dinner party acquaintances return to the saddle in Andalusia, they may find themselves picnicking beneath the cork oaks with the sort of people who usually spend their holidays in Benidorm. Which may prove an even more uncomfortable truth to bear.