Sorry to disagree here but I would go 240v all the way using proper IP rated lamps.
Most bricklights are IP 44 but the higher the better. You can get IP 65 ones and I wold only ever fit 65 or above unless I was forced to use a particular lamp. I agree water does can get in, even in IP rated units. Normally when people jetwash them down But the 12v or 240 the units will trip as you will either get a short to ground or between phase & neutral.
Plus you dont have to worry about transformers going down which they do as most people slightly overload them. Of course not everyone wants to spring to armoured cable or can actually fit it in situ so the individuals needs are what will determine.
I would also recommend GU10 fittings and then use LED or SGU10 lamps but most brick lights are Flourescents or ES. again just use low energy replacements - (flourescents are low energy).
I would avoid fittings that have inbuilt transformers. They will look nice for the next ten years or so but if one goes wrong you need to be repliant on spares or replacements of the same type or you're replacing all of them.
Of course being that they are outside you need to have a Part P sparks to install or sign off as it is notifiable work and thy must be protected by an RCD. If you go 12v and the transformer is located indoors (garage etc) then this isn't the case.
Other places to look for lights...
QVS - electrical wholesale like TLC
Toolstation - cheaper generally than Screwfix (owned by wickes)
National Lighting - good range, cheap, good quality and most of their units include lamps BUT careful they charge up to 30% re-stocking fee - so make sure if you buy from them its right.
