It is a sign of the times: even roller-coasters are to make allowances for children's bulging waists. The first theme park ride with outsized seats - and special seatbelts - are to open this week.

The 'big boy' seats will mean that no one, however hefty, will be excluded from a new £3 million ride in Staffordshire. Or, as its German makers put it plainly in the promotional literature: 'This seat has been developed to suit the needs of corpulent riders.'

The roller-coaster - called G Force - at Drayton Manor theme park, near Tamworth, does away with traditional shoulder restraints and pins people in their seats at the hip, leaving the rest of the body dangling free. But to maximise its use the designers had to make allowances for the fact that more than half the British population is now overweight or obese.

The ride will feature one larger seat with a wider locking mechanism at the back of a six-seater train. G Force spins its riders around under a gravitational force of 4.3 at speeds of more than 40mph.

Andy Hine, chairman of the Roller-coaster Club of Great Britain, said: 'I have a lot of members who are larger and get very upset when they get to a park and queue for two hours and are told they can't get on a ride.

'The designers are doing the right thing. I've seen the embarrassment when people who are not necessarily large, not obese, can't do the seat-belt up. The size of people is getting bigger, and at last someone is addressing that. These are the first special big-boy seats in the world.'

A special seat for the heftier man or woman is probably less humiliating than what happens in American theme parks, where would-be riders sit in a sample chair and try to lock the restraints. If they don't fit, the people are turned away.

The basic problem is that children and adults on both sides of the Atlantic are getting much larger. Planes have started to offer wider seats to some passengers, and in America some restaurants are installing much larger seats after finding that customers wouldn't come back if they found the chairs too narrow. Helen O'Neill, the Drayton Manor spokeswoman, said: 'We are having to design bigger seating for bigger people. We appear to be going the same way as America.'

But the term 'big boy' seat was not ideal. 'We will have to come up with a more acceptable term. Maybe "the fuller figure" is better.'