you need to get the authorisation to apply to BCA for the plans search first.
once BCA has completed the search, they will let you download all the plans for the house for preview. after previewing the plans, you can then choose which set you want to buy. the purchased plans are exactly the same as the preview plans just that the watermarks are different. you can't use the preview plans later for submission as the PE will require the BCA plans with the proper watermarks for submission