Royal Mail shippping - limiting services by size

The royal mail shipping method works well, apart from one issue, it does not take the item size into consideration

for example, i have a product that is a large enough box to need to be shipped as a small parcel, yet the module as currently offers standard 1st class stamp as a postage option

rest of the module works great, if there was a way to on the admin page but the max dimesions of each service (which is available from post office themselves) and then use the item size to limit the postage options

I know working out cubing or multiple items would be more of a challenge, but it would make a massive improvement if it would even do it based on standard product size

Hope others would find this feature request useful
Thanks
Phil

I've had a number of people use my Formula-Based Shipping extension to create Royal Mail rates with success. It can do dimension, weight, and volume criteria for the rates, so you can create different ones based on the items in the cart.