I doubt that's going to be satisfactory. Converting lawn to veg growing really requires double digging, with inverted turf buried at the bottom of each trench or used as the basis for a compost heap. Double digging also gives the opportunity to feed/improve the soil, especially as it's clay; mixing in barrowfuls of stable manure/seaweed/compost as you go along.
3m x 5m should take a day, maybe two tops, and getting it right at the start will save time later.
Assuming you don't expect to get all your acre producing veg immediately, cover areas you're coming to later with carpet offcuts to kill the turf. And if the plan is to get an acre of veg going asap then ignore all advice about double digging, and rotavators, and get a friendly local farmer to come and plough you over to start with.