In reply to Gabe Oliver:
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> So im thinking of buying myself a set of half/double/twin ropes (not sure which one really)
>
Half and twin ropes are different things. Twin ropes are intended to always be used together. They can be very thin indeed - thinnest are currently the Edelrid Flycatcher at 6.9mm - and are not intended to be clipped separately. They are useful in the Alps for routes with long abseil descents but are hardly ever used for UK trad climbing.
What you almost certainly want are half ropes that are intended to be clipped separately. (Some half ropes are also rated for use as twins, but that's of no interest to you if you're focused on UK trad)