I know this is almost a decade late, but the jumpers are from a UK manufacturer called John Smedley. Their jumpers are the ones Eccleston wore exclusively (fairly thin wool with ribbed v-neck collars and ribbed cuffs), and they're very expensive, especially for a cosplay item (starting at about £125.00 UK).
There are other, more affordable options that are close enough for government work, as they say: St John's Bay, The Territory Ahead, Hanes, and Haggar all make/sell thin-ish jumpers here in the US and are all good proxies for Eccleston's wardrobe. A trip to your local resale shop, or even scoping out eBay should yield some good and affordable choices.
The one that's the Holy Grail, though, is the green jumper with the seam down the centre (first seen in 'Dalek'). As the Smedley jumpers were/are seasonal, it's nigh impossible to find that particular style, so if that's the one you're going for, locate a good ersatz jumper in the right colour, or at least close enough, and have a tailor put the seam down the centre for you.
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