Child Maintenance Service (The Child Support Agency is part of the Child Maintenance and Enforcement Commission. Its role is to make sure that parents who live apart from their children contribute financially to their upkeep by paying child maintenance.
You may not always have family service nearby but these are your nearest sexual health and family planning centres serving London
National Council for One Parent Families in England and Wales
Support for one parent families in Scotland. Runs the National Lone Parent Helpline for advice and help. Freephone 0808 801 0323
Local social services and Welfare Organisations serving the area around London and London
HMRC Website - another 'snappy' government site with everything there if you can keep at it!