What actually is Trionium, anyway? Easy: Trionium is the hardest stuff known to man...

Trionium events

Trionium events aim to be among the best in their field....


The Trionium Leith Hill Half Marathon was voted the Best Race in Britain in 2015 (Runner's World February 2016).

All of the Trionium races (and the Ashtead 10k) were named in Runner's World 2014 Top 50 best races in the UK listing (February 2015), apart from the Greensand Marathon, which should have been included at around position 20, but which was erroneously left out of the list. D'Oh! In 2014, the Knacker Cracker was in 38th place, Ashtead 10k (30th), Bath Hilly Half (26th), Midsummer Munro (23rd), The Picnic (22nd) and the Leith Hill Half was in 9th place.

In 2013 Trionium organised the UK's top two trail races (knacker Cracker and Midsummer Munro), a top 3 half marathon (Leith Hill Half) and a top 5 marathon (Greensand) according to Runner's World (February 2014).

Trionium organised the UK's top trail race (Knacker Cracker) and another top 10 trail race (Bath Hilly Half), England's top half marathon (Leith Hill Half), a top 10 marathon (Greensand), and two top 10 'Ultras' (Picnic and Midsummer Munro) in 2012 according to Runner's World (February 2013).

Trionium organised the UK's top-rated trail races (Picnic Marathon and Midsummer Munro half) and adventure race (UK Wife Carrying Race) in 2011, according to Runner's World (February 2012).

Trionium organised the top-rated 10k (Knacker Cracker) and marathon (Greensand) in 2010, as well as two of the top three best half marathons in the UK, according to Runners' World (February 2011).

Trionium races won five places in the top 20 races in Britain in 2009, including the top-rated 10k (Knacker Cracker) and the top-rated marathon (The Picnic) - (RW).

The Greensand Marathon won the Best New Event at the Runner's World Personal Best Awards 2010.

Runner's World no longer names its best races in the UK.

The Midsummer Munro was voted best race in Britain 2008, and in 2011 was named one of the top 500 races in the world.

Trionium events aim to be as safe as possible (notwithstanding inherent risks)...

Trionium events are organised and marshalled by volunteers....

Trionium events are friendly, enjoyable and informal....

Conferio Ltd may charge a per person fee (included in the race entry fee) for the organisation of all Trionium Races, excluding Trionium-affiliated races.

All monies after expenses are donated to charity: The Trionium races have donated over £69,756.68 to charity since the first Knacker Cracker race on 1 January 2004 (to 31 January 2023), not including 15,201 raised by the Ashtead 10k.

The Future of Trionium events

The original Trionium event was on 1 January 2004.

Rob McCaffrey, race organiser, decided at some point that he'd raise £100,000 for charity (getting there), and/or organise at least 100 events (tick) and/or organise them for 20 years.

1 January 2024 will mark the 20th anniversary of the first Trionium event - the original Trionium Box Hill Knacker Cracker (with only 18 entrants!).

We have had many wonderful days organising the Trionium races - many, many great days and many wonderful memories, with well over 10,000 different competitors having taken part in the Trionium events.

The Knacker Cracker on 1 January 2024 will be the final Trionium Knacker Cracker, and it will then be handed over to new organisers; the Trionium Leith Hill Half half marathon on 17 March 2024 and Trionium Midsummer Munro on 23 June 2024 will also be the final editions organised by Trionium, and each will be handed on to new organisers - the races will continue! 

The Ashtead 10k is organised in a slightly different way, and will continue as it always has.

Comments? Please email rob@trionium.com


Dog policy

We welcome well-behaved dogs to our races, on the following provisos:

• Please confirm that you have public liability insurance for your dog to the race organiser, rob@trionium.com. Many household policies provide liability insurance for dogs as do many specific pet insurance policies.
• Dogs should be on a lead using a CaniX regulation waistbelt at all times
• Owners should clean up after their dog (otherwise it's a DQ!)
• Runners with a dog must start at the back of the field.

Troll policy
Trolls will be banned, deleted, cancelled, blocked, turned off (etc). Please take your negativity elsewhere!

Trionium race terms and conditions

Privacy Policy


Trionium Magazine is published by Conferio Ltd.

Trionium Magazine covers running, swimming, cycling, MTB, triathlon, adventure racing, sailing, climbing, active holidays. expeditions, drinking, eating, sex....and all that jazz!

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Issue 4 will be available whenever we get the time to put it together!

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Conferio Ltd

Company No. 05335958, England and Wales.

Registered office:

Conferio Ltd
Ground Floor, Octagon House
20 Hook Road,
KT19 8TR

info at trionium dot com