" Well - I wouldn't use an architect as you'll pay through the nose. "
Have a
from an architect!
" I would use a technician with experience of planning & building regs & go by recommendation. They are just as good as RIBA architects and a whole lot cheaper. "
And another
for good measure.
LittleMilla the title 'architect' is protected by law however (unlike many countries) the design of buildings, alterations etc. is not protected so almost anyone can deem themselves 'qualified' to design your extension.
I don't know why PorkyandBess has such a jaundiced opinion of architects but be assured we are not all overpriced and are actually qualified to practice architecture rather than simply draw plans.
Having said that (and getting off my high horse for a moment) a technician, technologist or RICS surveyor may be perfectly able to provide the drawings for a simple extension and may very well charge less.
This is not an advert but as far as my practice is concerned I provide a free initial consultation (provided the client is not too far away) of around an hour or so which allows for a dialogue, the chance to esplore some ideas and maybe a few sketches as well. The inclusion of wine nice coffee and possibly biscuits encourages a longer and more friendly discourse! 
Should the project be simple in nature - e.g. flat roofed, no planning or listed building consents required, no 'odd' Party Wall problems etc. I have been known to charge as little as £800 for plans, elevations, sections, site and location plan and sufficient detail for a building regs submission. I have even been known to fill in the application form for the client (although they submit and pay the charges). Included in the fee are any minor amendments necessary to ensure the application gets consent.
Architects receive - up to a point - training in structural design so I often undertake simple calculations myself however I know many in my profession fear and loathe anything to do with structures. If I need an engineer then I use a few trusted locals who usually keep their fees to a few hundred pounds. I have never come across the " £80 a steel " engineer though!
If the client wants additional services then I can provide a detailed construction drawing and a specification, manage a tender exercise, and administer the contract. Most domestic clients are happy to simply take the consent and manage their own tender and builder. Almost every commercial or public sector client goes for the 'full' service.
As I said, this is not an advert but I am sure a few telephne calls will find you a local 'Pendeen' who can help realise your aspirations without having to " pay through the nose "
Best wishes.