The first person to write to should be your MP or your midwife's MP.
You can locate their details and send them an email via an online form here.
You can also email MPs through WriteToThem.com  

Or via the BBC News MP Database you can find their email address as well as constituency address.

Bear in mind that real letters tend to get politician's attention better then emails, and writing to their constituency address is reckoned to be preferable to writing them at Parliament.

Other influential people are: 

Rt Hon Alan Johnson MP - Secretary of State for Health, Richmond House,
79 Whitehall, London. SW1A 2NS

Andrew Lansley CBE MP - Shadow Secretary of State for Health, House of
Commons, London. SW1A 0AA

John Baron MP - Shadow Minister of Health, House of Commons, London. SW1A 0AA

Norman Lamb MP - Liberal Democrat Shadow Secretary of State for Health, House
of Commons, London SW1A 0AA

Ivan Lewis MP  Parliamentary Under-Secretary of State for Health, House of Commons, London SW1A 0AA

Christine Beasley - Chief Nursing Officer, Department of Health, Richmond
House, 79 Whitehall, London SW1A 2NS

Caroline Simpson - Professional Adviser, Maternity and Family Health,
Department of Health, Room 330B Skipton House, 80 London Road, London SE1
6LH

Sarah Thewlis - Chief Executive, Nursing and Midwifery Council, 23 Portland
Place, London W1B 1PZ

Christina McKenzie - Head of Midwifery, Nursing and Midwifery Council, 23
Portland Place, London W1B 1PZ

Professor Paul Lewis - Chair Midwifery Committee, Nursing and Midwifery
Council, 23 Portland Place, London W1B 1PZ

Sandra Arthur - President, Nursing and Midwifery Council, 23 Portland Place,
London W1B 1PZ

Karlene Davis - General Secretary, Royal College of Midwives, 15 Mansfield
Street, London W1G 9NH

Mary Newburn - The National Childbirth Trust, Alexandra House, Oldham
Terrace, Acton, London W3 6NH

Peter Vicary-Smith - Chief Executive, Head Office, Consumers Association, 2
Marylebone Road, London NW1 4DF

Dr Sheila Shribman - National Clinical Director for Children, Young People and Maternity Services, 79 Richmond House, Whitehall, London SW1A 2NS

Paul Martin, Chief Nursing Officer, Health Department, Scottish Executive, St Andrews House, Regent Road, Edinburgh EH1 3DG

Nicola Sturgeon, Minister for Health, Scottish Parliament, Edinburgh EH99 1SP

Shona Robison, Minister for Public Health, Scottish Parliament, Edinburgh EH99 1SP

Dr Margaret McGuire, Midwifery Officer, Health Department, Scottish Executive, St Andrews House, Regent Road, Edinburgh EH1 3DG

Rosemary Kennedy, Chief Nursing Officer, Welsh Assembly Government, Cathay’s Park, Cardiff CF10 3 HQ

Polly Ferguson, Nursing Officer for Womens’s Reproductive Health, Welsh Assembly Government, Cardiff CF10 3NQ

Robyn Philips, Midwifery Advisor, Health Inspectorate Wales, Bevan House, Caerphilly Business Park, Van Road, Caerphilly CF83 3ED