A Yes. Adidas.co.uk have published a six-step guide to returning orders placed with the webstore.
Currently consumers have one hundred days to return products; except for 'mi' customised shoes and apparel, which cannot be returned - these are products where consumers pick a specific colour scheme for a select range of shoes and track suit tops. Adidas state that refunds will be issued within fourteen days and should include the delivery costs of the order; the refund will be dependent on the quality of the return product, and whether the condition is deemed good enough to warrant a refund. If gift vouchers were used, then the full amount should also be reimbursed; however, the small print of certain vouchers and promotions may indicate that a refund is not possible; you will need to double check the small print. Exchanges are not currently possible with UK webstore orders; you will have to order the product you want with the refund issued for the original product.