hi roger we would be able to all depending where you are based. let me no,,,,,,

Any recommendations for a structural engineer to do drawings and Calcs for a loft conversion and rear extension in south London

As for me, the most important thing is the civil engineer. He needs to make all calculations for technical changes, taking into account the likely load and the use of specific materials. He may also suggest making changes that can make the project cheaper or more expensive. Honestly, I always thought that it would be easier to look for such a specialist through the architect's office, even if you already have a finished design project. I know that these companies only hire employees with a good resume like this example - https://resumewritinglab.com/construction-resume-writing-service.html There are no random people without experience. And it also gives you additional guarantees on the quality of the work performed.

An architect designs buildings. A structural engineer works out the mathematics of how that building will stand. If you want someone to design the new part as well the existing part you need an architect. If there are structural changes the architect will hire a structural engineer to work out how those changes can be done. Once the design and structural calculations have been done the architect will put them together and submit the planning and building regs applications for you.