Expenses must be incurred wholly and exclusively for the purposes of the business. You can claim for vehicle expenses, train, bus car and air fares, the cost of hotels and other overnight accommodation and the cost of meals. You cannot claim for non-business driving or travel costs, fines (such as parking fines) or for travel between home and work. Be careful of expenses which could be said to be duel purpose.
Business travel and related subsistence and accommodation expenses are usually allowable for tax purposes. Consider the type of journey, the trades and where the business is run. Where a journey is both business and private then claim the business element only. Travel from home can be claimed where you are based from home. HMRC may resist a claim if there is another operational base or bases (site, hospital, office, shop, yard, sales area etc).
For subcontractors, HMRC may insist that the operational base is the site where work is undertaken. Ensure contracts/paperwork are undertaken made from home and tools are stored there. In the case of Notion v Young (1971) 47 TC 60, a bricklayer worked on a number of sites within a certain radius of his home for a few weeks at a time. It was held that his home was the base of his operations.