Biteback for horses Mudbar cream is outstanding!! Cannot recommend it highly enough, cleared up all traces of mud fever from our two within 3 weeks. It is a simple cream that you put on and you can get different strengths -MudbarPlus being the strongest, fastest acting (and most expensive!) one.
CustomXC do cross-country base layers that you design which are £39. They also do cross-country polo shirts. Treehouse do an Event shirt but they are pretty expensive!