Jonathan, offer babysitting in London EC3N

We're hoping to find a sitter who might have occasional availability between the end of school (15:00ish) to early/mid evening to look after our 11 year old son, when we're not able to get home from work. We would ideally like to find a single sitter who could do this for us for a maximum of once or twice a week, to minimum of once or twice a month depending on our work schedules. We have one date that is in definite need of cover, the 3rd of March, and so would like to have someone in place by then. Thanks for reading. Jonny