Hot off the press from the UK government. We needed the clarification of the definition of transit and we now have it. This is correct at the time of publishing it. The link to the page is Entry requirements - Switzerland travel advice - GOV.UK (www.gov.uk) then specifically refer to the 'transit' section.
Following the update of a Swiss ordinance on 30 November, there is no quarantine requirement for travellers arriving in Switzerland from the UK who wish to travel onward to another country, as long as travel through Switzerland is less than 24 hours and does not involve a stopover. More detail is available in the ordinance (in English) and in German. There is no quarantine requirement for those in transit airside at the airport.
If you are transiting Switzerland, you are strongly advised to have your onward travel booked in advance and to have confirmed you meet the entry requirements of your destination country (you may be asked to provide proof of your onward travel and accommodation). If you are transiting by air, you must complete an online form and provide contact details. You should also check the travel advice for any country that you will transit on the way back to the UK. Further information about travelling through Switzerland is available from the State Secretariat for Migration.