Do you need an architect to do plans for a standard loft conversion or do some companies do the drawings for you?

[GoneForGoodies]

We're in London and probably going to use one of the big companies like MoreSpace or SMA.
Do they do the drawings as part of the contract or do you need to get drawings done separately by an architect?

Usually the loft conversion companies have surveyors and architects who do the drawings for you. We looked into both options (so getting our own architect or getting the loft people to do it) and the architect option worked out more expensive (By about 2k - 3k) so we've just gone with the loft conversion company.

I looked at both options but found the companies like plus rooms had such an expensive build cost. I used a spilt company architect & they had a recommendation for a builder and I was really happy with my result.
www.hometales.co.uk and www.homeconstructive.com for the build.