Two of them arrived on identical bicycles, sporting identical helmets and matching rucksacks.

Another pair stayed so close they barely strayed apart by more than a couple of paces.

And some of them have had a spooky idea about what the other was about to say, before she even said it.

Today, some of these intriguing links were finally explored at a record-breaking gathering of twins taking part in the world’s biggest medical study.

Runs in the family: Twins Helen Watson, left, and Janet Barron, right, with Janet’s twins Maisy, left, and Isla, right, at St. Thomas’ Hospital to celebrate the genetic research of twins over the last 21 years

Paired up: Seven sets of twins from London who have taken part in the Kings College twins research programme which is celebrating it 21st anniversary this weekend

Record breaking: Hundreds of pairs of twins gather in the grounds of St. Thomas’ Hospital in London to celebrate genetic research of twins today

Mirror image: Twins relax in the grounds of St. Thomas’ Hospital where important research has been carried out into the genetics of twins

Twins Carole Dempster, left, and Jayne Brocklehurst, right, pictured at the 21st anniversary event

All in attendance: From left to right are twins Janet and Janese, Hazel and Christine, Margaret and Barbara, Rebecca and Zoe, Gemma and Nadine at the celebratory event

Around 750 individuals (that’s 375 pairs in anyone else’s language) assembled to celebrate 21 years of research by the Department of Twin Research at King’s College, London, based at St Thomas’ Hospital.

More than 12,000 twins aged between 16 and 101 are registered for the study, which has helped experts to catalogue a series of findings that range from the mildly fascinating, such as twins drink an average 24 cups of tea a week and like Marmite, to potentially ground-breaking discoveries.

They include scientists discovering more than 400 novel genes associated with over 30 diseases since the study began in 1992, enabling researchers to investigate genetic and environmental causes of traits and illnesses including cancer, short-sightedness, osteoporosis, pain, diabetes and obesity.

Research: Twins receive dance tuition in the grounds of St. Thomas’ Hospital to test their co-ordination

Progress: The ongoing research into twins at St Thomas’ Hospital, pictured today, has helped scientists to identify over 400 genes associated with more than 30 diseases

Young recruits: Twins Davina Bond, left, and Sabena Bond, right, also took part in the event held by the Department of Twin Research at King’s College London which is based at St. Thomas’ Hospital

Sister act: Twins Janese Samuels, left, and Janet Morgan, right, pictured at the event celebrating the genetic research of twins

Spitting image: The research into twins including Diana Bartholomew, left, and Sandra Horner, right, has helped to identify genes which are connected to diseases

Today’s birthday event saw 750 taking part in scientific experiments for research into areas such as pain, hearing loss and skin-ageing – as well as undergoing a telepathy study.

Participating twins were separated; one was subjected to minor electric shocks or sudden loud noises while the other was asked if they experienced the same reactions.

TwinsUK director Professor Tim Spector said other tests included sitting twins opposite each other and asking them to guess which cards the other is holding.

Prof Spector, who is sceptical about claims of telepathic communication between twins, said: ‘Last time we did this, the only clear result was that those wearing reflective sunglasses cheated.’

Double act: Twins Elizabeth Canning, left, and Theresa Banister, right, are just one set of 12,000 twins on the TwinsUK registry

Sets of twins relax in the sunshine today in the grounds of St. Thomas’ Hospital for the anniversary event

Making a difference: Seven sets of twins from London who have taken part in the Kings College twins research programme which is celebrating it 21st anniversary this weekend

Doubling up: Twins Jenny Carrick, left, and Jeanette Carrick, right, pose for a photograph in the grounds of St. Thomas’ Hospital today

Life-long bond: Twins Joan Robbens, left, and Joyce Shuter, right, took part in the gene research

Read more: Daily News