Who pays for the Pack?
The seller is responsible for the cost of a Home Information Pack. The cost of the Pack is down to the market, but sellers will often be able to defer costs until late in the sale.
How will I pay for the Pack?
This depends on the agreement between the seller and the compiler of the Pack. Some examples of the ways that Packs might be paid for are as follows:
Seller pays for the Pack upfront from estate agent, solicitor or Pack provider
Seller compiles the Pack and pays each organisation for the relevant component (e.g. the Land Registry for the title document)
Estate agent offers the Pack to the seller on a 'no sale, no fee' basis, where the cost of the Pack could be included in the estate agent's commission
Estate agent offers the Pack to the seller on a 'buy now, pay on completion' basis, which is usually a credit agreement for three or six months between the seller and the organisation compiling the pack.
These are only indications of payment models; the Pack regulations do not prescribe any particular payment method.
From the HIPS website.

