Hello!
Former Criminal Barrister in England here..
Feel free to ask me anything.
In short for OP.. almost all criminal defence work is via legal aid. A privately paying client would have to go through the standard solicitor money laundering regs but Barristers aren't ever involved in the payment side directly that's all via solicitors (except in very specific situations).
For everyone else.. most criminal Barristers both prosecute and defend. If you didn't have us defend you wouldn't have any prosecutors to send the bad people to jail. We are also bound by the cab rank rule and are legally obligated to take any case you are competent to undertake and available to take. You cannot say I won't defend x offence or y person.
If a client tells you they are guilty you cannot represent them on a not guilty plea and at trial.
People always fall back on the "but you just know".. well obviously at times you know the evidence is strong and their account is unlikely. In these circumstances they will inevitably be convicted. However I have also appeared in many cases where my reaction was the client was guilty until 5 minutes after the first witness gave their evidence and it becomes abundantly clear they aren't truthful. In short you literally never know.
People make the mistake of thinking that criminal defence exists only for bad people. If the current age tells us anything its that allegations are easy to make. I once prosecuted a lady who ultimately admitted making false sexual allegations about a taxi driver..
Anyone can be the subject of a false allegation and if that's unlucky enough to be you you'll be grateful for a skilled and experienced criminal barrister.
No we would not happily let child murderers walk free for the money. Legal aid rates are pretty terrible for the reasons a precious poster set out. You get a fixed fee for the preparation and first day of a trial. You don't get paid at all for the second day of a trial. You don't get paid to meet you client in advance of court to take their instructions. If you prepare a case which then is adjourned for lack of court time and it is then resisted to a date you are unavailable you don't get paid a penny for your preparation no matter if it took you days.
The defence lawyer doesn't decide who is guilty or not. That's a jury or a judge's job.
And yes it is mighty embarrassing when you stand up to give a speech in an utterly hopeless case and the jury look at you like you're a prize tit.