Ano Nymous

Hi, I have a related situation. I am a sole proprietor providing software development consulting. My company is registered in Finland, my home country, where I live permanently with my family. I am negotiating with a company that has offices in London to consult for them on site in London for three months through my company. The turnover for this arrangement would not exceed the £90,000 VAT threshold and I would be in the UK for less than 90 days. First of all, does the reverse charge apply to the above arrangement? Do I need to register for VAT? Perhaps a key question is whether (temporarily) consulting on site for three months constitutes a "fixed establishment". The UK company is also approved and willing to provide a "certificate of sponsorship" (CoS) for a visa. Thank you.