There are loads of plan drawing services that will do this sort of thing for a fraction of the price of an architect. Look in yellow pages.

in majority of cases you dont need planning to build an extension ..under permitted development you may construct an extension to rear ..and side in some cases ..outwards 3 metres ..4 if detached ..and full width of property ..either single or two storey ..without any planning needed ..but for next 3 years you can apply for double the size ..and providing the neighbours agree you can get planning without going through committe ..save your money

They will want design plans and possibly structural calculations to approve. If you can do that, you do not need an architect.

I am looking to sell my property and someone has suggested to me that it may be good just to get planning permission for an extension, to include as a sort of incentive when putting the property on the market, will I need architect drawings to put in with the application or can I just apply for the standard planning permission that costs ￡172 on planning portal.

Many thanks in advance.