Non-visa nationals can usually enter the UK as a Standard Visitor for a short business trip covering trade-show attendance; visa nationals must obtain a Standard Visitor visa before travelling. Check your nationality on GOV.UK before booking.
Estimated cost: Standard Visitor visa fee per the current GOV.UK fee schedule; check before applying.
Processing: Allow several weeks for a Standard Visitor decision from a complete application; confirm current published processing times on GOV.UK before committing to travel.
Business visitor status allows attending the show and commercial discussions but not paid employment. Bring registration confirmation, hotel booking and a return ticket, and check the GOV.UK visa requirement list for your passport.
Official