//The UK has been a "member" of the WTO since 1948 and gained "Accession in 1985.//
The WTO came into existence 1st January 1995; one of its 124 founding nations was the UK.
The WTO is the successor organisation of the General Agreement on Tariffs and Trade (GATT), a multinational treaty signed by 23 countries on 30th October 1947 to come into effect 1st January 1948, on which date eight signatory nations activated GATT and its tariff concessions:
United Kingdom,
United States,
Australia,
Belgium,
Canada,
France,
Luxembourg,
Netherlands.
//But the WTO complaints panel do act quickly: Boeing and Airbus have only been in dispute for 14 years - still unresolved.//
You do realise that the only disputes involving the UK are complaints made by parties against the EC/EU.
https://www.wto.org/english/thewto_e/countries_e/united_kingdom_e.htm