POrobably best setting up as a sole trader or a GmbH company in Switzerladn and invoicing your UK clients via this route. A little depens on the amounts you are talking about, my guess is you would need a minimum of Chf100k turnover to justify a Swiss company.

You will pay tax here as Switzerland is your domicile. With a company you can deduct all your expenses, such as flight back to the UK for client consultation (guess you're lucky if this coincides with your sisters wedding....)