I used to attend business exhibitions in London. Thanks to the mayor (Sadiq Khan) and his TfL tax on visitors I avoid going to any exhibition located in the Ultra Low Emission Zone (ULEZ) of London. As his need for funding grows he expands the ULEZ to put more vehicles in scope, trying to justify it on health grounds.
Visiting London is expensive. The railway train fares are prohibitively expensive (£226 return advance booking + £13 tube) for travel during business hours. Car travel used to be an alternative, but the combination of increased fuel cost, car parking fees, Congestion Charge and TfL taxes make it less of an option.
Staying overnight in a hotel on an exhibition day currently is around £350 per night with advance booking.
The exhibition companies are fighting to regain attendees after the Covid-19 lockdowns. In London they fight against the inconvenience and tide of rising travel costs. For a 2 day trip by train from Derby to a large exhibition in London you are looking at around £600 - £700 including basic food.