RE: @direct debit
I too am a contractor with random pay dates.
One problem is that bills need to be paid, usually by a certain date regardless of how I have been paid. One of the points of contracting is that the increased rates are there to deal with things like late / random payments and unpaid times between contracts.
However, back to the point, what I did was to open a bank account purely for direct debits. It takes 1 month of jiggery-pokery initially to get the money in but after that as long as you pay the money in at some point during the month it does not matter when you get paid or when each direct debit is taken out.
You should have a pretty good idea as to what your DD outgoings will be so you can always check the account to make sure your outgoings will be honoured.
@Wayne, Regarding bank errors on DD, the bank is bound under the terms of the DD agreement to refund any errors. As long as you check your bills / payments (which you should) then if you find an error you just need to phone the bank and demand a refund. It is then up to them to chase it up and sort it out.