Once you have established a base for your business, be that home or an office, any travel on business away from that base can be charged as a legitimate business expense, so if you are travelling to an interview or travelling to and from your clients site to deliver the contract, all travel expenses incurred can be recovered.
In many instances, clients want to negotiate an all inclusive rate - that is a rate that coveres your costs of getting to the place of work and any accomodation costs that you incur in delivering your services. You need to build this into your negotiations on rates as it can have a big impact on your net income.
Once you have negotiated your fee, your skill will be to arrange your travel and accommodation as cheaply as you can. I'm not suggesting that you stay in the cheapest B&B in town (although many do), I'm suggesting that you negotiate with the hotel, or if you are on a longer term contractor, you may look to take a rental flat. Identify ways to reduce your expenditure to a minimum.
There are partner organisations that can help you source good deals on accommodation - hotels love regular custom and if you commit to a long term stay, you will be able to negotiate very good deals - just don't be afraid to ask.
Similarly on travel - if you can commit to your travel plans well in advance, many rail, coach and airlines offer some amazing deals. One trick many experienced contractors use especially when commuting into London by rail is to book their travel from London with a open return ticket. This is often far cheaper than it is to book a return ticket to London