Recommend an architect for any substantial renovation. They will come up with great ideas for light and flow that you will otherwise miss. You do have to take their advice however 😜 I would also suggest that you engage an architect whose previous work you like and with whom you have a rapport. This article will help. https://www.houzz.ie/magazine/what-happens-when-you-hire-a-professional-stsetivw-vs~159232511

To give a brief overview.

An architectural technician is generally a person whose background can vary dramatically from person to person. Some have had formal architecture training whereas others have a more technical background, and others are more drafts persons who have learned on the job. Unless you are very sure of what you want the design to be, I wouldn't recommend engaging a technician.

Interior designers usually have some formal interior design training (though not always the case). Generally speaking for interior design purposes they are usually be right on trend of the current interior styles and usually have a more intimate knowledge of interiors materials and usually quite good when it comes to colour composition.

Registered Architects have had formal training at university and have undergone formal training in aspects of planning, business management, project management etc. In the UK the term Architect is protected under law to provide the public with assurance registered Architects are competent. Architecture is a massively diverse field of practice with some Architects specialized in massive master planing whilst others focus on individual small buildings and interiors, and intimate knowledge of materials. It's important to engage an Architect with the right background and work.

(Not really sure what a concept planner is but most design professionals should be able to work on a concept level)

If you are looking to undertake renovation of an existing building, I would recommend engaging with an Architect who has experience with that type of work. A good Architect will be able to look at the building holistically and make intervention to maximize your space. You may also look at how to make your home more energy efficient and make interventions to the external envelope. If you engage an interior designer on a domestic scale project, the proposals may be limited to decor and minor interventions only and miss out on a potentially more meaningful changes for the long term.

Full disclosure, I am an Architect and I suppose biased, however in my view an Architect will be best suited for your needs.

Architects are exceptionally well qualified in design and how to get the best out of a building. In my experience they are not always as budget conscious as they should be. Many a person has consulted them to come away with a fantastic unaffordable design. Architectural Technicians are not as well qualified as full architects but may be able to help you a great deal with designs and visualisation of the finished house. Structural engineers will stop your building falling down. If you remove internal walls they will do the calculations of the replacment supports required. Interior designers deal with finishes but not building structures and are usually consulted later. If you wish to save money I woulds start with an architect or architectural tecnician followed probably inevitably by a structural engineer if wall removal is required you can save money by only paying the architect for the drawings. You will have to liase with the builder and project manage yourself. Seasoned renovators might be able to work with a builder bypassing these steps but you will not get the benefit of an architect's superior building design knowledge. They spend many years at uni for a reason. I have never heard of a concept planner either.

Given you only want to ”perhaps change the layout” I’m not sure if a qualified interior designer is a better option in this instance preferably someone who passes on their trade discounts for a full renovation! They often work alongside various trades and can project manage the whole renovation too.

Why not post the plan on here for comments as it could be a concept planner can help with kitchen, bathroom etc layouts too. It really depends on how involved you want to be re the interior design. OnePlan on here is highly recommended if you go the concept planner route

Yes, post that floorplan and a google sat screenshot! Tell us what you'd like to achieve. Bring on the goodies!