I have just been speaking to the tax credit helpline. H and I are separating soon and I knew I would have to make a new claim as a single parent. They have just told me that they have a dedicated phone line just for people having to change from a joint to a single claim as they understand that this almost always means a lack of income
Apparently if you are changing from a single to a joint or are making your first claim you have to be sent an application form, which can take 2 weeks but not if you are going from joint to single, meaning you save that 2 weeks
Oh and this line is open an a saturday!