I have no idea about aviation companies for this sort of thing but I used to do a similar thing when I worked in IT. You can either set up your own limited company, or work under someone else's umbrella company. I used a company called parasol (get it? big umbrella!). They were pretty good, I just invoiced them and gave them details of all the expenses I had incurred. They then invoiced the client and all expenses were offset against the income tax.
Parasol - Umbrella Companies | PAYE umbrella company | best advice