There are a lot of if's with things like this but to start with you 'shouldn't' need an architect if its just taking walls down and remodelling inside:

An interior designer can help but you'd need to make sure they offer space planning, if they don't they will probably not touch it until the walls are down, or if they do will want nothing to do with taking the walls down.

Most building companies (If they are a company and not just a lone builder) should be able to quote to take the walls out but:

It depends on what the walls are (and if you house is listed, I'm assuming not) If they're stud they can come out no problem BUT if they're masonry that's harder and if they're load bearing it gets much more complicated with beams and building inspections (Again, a builders company should be able to handle all that for you)

Knock on the walls; if they sound hollow they're probably stud, if they sound solid they're probably brick, if there are brick walls directly above them then they are definitely load bearing, If you can find which way the beams run you can work out if they are bearing the floors or not.

If you know exactly what you want to do with the space once its opened you can probably talk to a builder, they should be able to do drawings and may be able to do all the decoration etc. to make the room how you want.

If you're not sure what you want exactly or what options to choose an interior designer or an architect would be a good start, architects are usual more expensive and would be a bit over qualified for just taking two walls down but as I said an interior designer would need to offer space planning not just interior design. Some building companies will also offer some design advice but it might be a bit limited.

I offer both design and space planning along with 3D digital modelling so clients can see what a room will look like before anything is done as well as remote working (shameless plug) Do you know what it is you want to do with this new room?

Why would you get rid of a utility bootroom? These are great! Multifunctional (and less noises from central heater, washing machine, freezer), no shoes in the rest of the house and so on.

You just need a general builder to start with.
They will give you a quote for removing a wall, installing a steel, moving radiators, rewiring, plastering and making good. Later on you may need a structural engineer to tell the builder exactly what steel to use in order to meet regulations. During the build you will need a local authority inspection. A competent builder can arrange the structural engineer and building regs.... you need to be clear you expect him to do so.

As far as finishing touches like new kitchen, flooring window treatments it’s worth doing research early on. This means you know what it’s going to cost to achieve the finished look.... it might also change your perspective of what you want the builder to do.... for instance blocking the utility room window might make planning the kitchen easier. There are lots of professionals who can help with this part of the planning including designers, interior designers, concept planners and independent kitchen retailers.