I am writing to a lab in UK to ask if I can volunteer there, but am having troubles with writing as want to make good first impression. How much personal detail should I include? Right now a have a short letter just saying who I am, how interesting their work is and can I join them.

Then I have put a short CV, a list of courses I have attended and a short "letter" where I speak about what I want do in the future etc.
Is this too much or too little? It is a good lab, so I really want them to see how much I'd like to go there, and how it would fit exactly with my plans.

I would just send a CV like you have mentioned and a single letter of application (probably about 1 A4 sheet), saying who you are, why you want to work there and why they should take you on.

Good luck!
Jo x

Thanks Joey! I wanted to use two lettes - a short actual message and than a longer letter as an attachment, but perhaps it's better to make it just one like you said.

Oh, and something else, how many references should I include? Should I just write their contact info, or should I ask if they could write something for me, or should I tell my potential "employer" that I can arrange letters of recommendation if he wishes me to?

I would include the names and contact details of 2 referees - make sure you ask them first if they are willing to provide you with a reference if needed!

I put my references in a section at the end of my CV, think is the normal place to put them!

Joey, you've been such a great help. I really appreciate it.

No probs! Not saying my way is the right way so if you would rather write 2 letters go for it! Good luck x