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Travers Smith if that's what you mean
Written exercise: There is some basic maths involved to work out a factual answer before you write a longer piece. The maths is not difficult so don't let it throw you even if you think you're not good at maths. Make sure you get the right answer (but it's very time pressured so there is a balance between making sure you're right and getting on with the actual writing). Write as clearly as you can not using legal jargon and try to finish to show you've planned your time but don't panic if you don't (lots of people won't).
Interview: Commercial aspect and competency questions. For the commercial bit, try to pre-empt the questions and read it carefully. It shouldn't be too alien and is quite clear. The competency questions seem quite odd, think there's a list that they just stick to and none of them will be much of a surprise but it isn't very spontaneous. There is the classic why law, why here, commercial story that interests you... be prepared to be challenged on these so have solid answers.
Group exercise: Is commercial in nature unlike some firms but again very accessible. Do the usual not talking over anyone or being too dominant but making sure you say something. Try to only speak when you have a useful point or suggestion as they will see through meaningless fillers.
There are quite a lot of people there, but don't let it put you off. Is quite a friendly vibe. Think you spend a bit of time sitting with a trainee if I remember rightly- be nice obviously as it's not assessed but they may just say oh I liked him/her or no I didn't. Overall it's a fun day and a good level of challenging.