I see a recommendation in the UK government guidance to go through an agency, but how reputable are the agencies? I assume they're not charities but businesses, so what ethical framework do they work under, if any? Are they primarily looking out for the intending parents or the woman who's going to go through the pregnancy?
In the UK it is illegal to advertise for or to be a surrogate, to match surrogates with intended parents, or to profit from surrogacy.
The two main UK organisations are COTS (Childlessness Overcome Through Surrogacy) and Surrogacy UK. I realise I keep mentioning the same groups, but it's because they are by far the oldest and most experienced. COTS was founded in 1988, Surrogacy UK in 2002. Both are non-commercial, not-for-profit organisations.
COTS introduce their website by saying "COTS is NOT an American style commercial surrogacy agency. Our prime objective is to pass on our collective experience to surrogates and would be parents". Support is through the online community, and dedicated support workers for intended parents and surrogates. There is also counselling support, medical support (from a Nurse Consultant for CREATE Fertility Manchester) and legal support.
Surrogacy UK has a board of trustees, an advisory board, office staff, and dozens of volunteers (e.g. support workers) giving back to the organisation. Among these people and the whole membership there is a wealth of surrogacy experience whether as a surrogate or intended parent. There is also an ethics committee made up of an independent group of experts from various relevant fields such as pyschology, law and medicine.