Open up internal door way from kitchen - need building regs?

[Gotaquestion]

If I wish to make an existing internal doorway wider (currently approx 75cm door width and I would double this).
The current door leads from the kitchen to the dining room. House is new build (6 yrs) and on two floors only.

Does this require building regs ?

I have an estimate from a builder and his view is there is no need for building regs as there is an internal door way already and both rooms are habitable - but I wondered if there is any issue that applies because this is from a kitchen.

He has said he cannot see any need to imploy a structural engineer -but he can arrange one if need be at my expense.
The wall is blockwork (all downstairs walls are blockwork with dot and dab plasterboard) and he proposes to leave a 150mm retaining nib and fit a new lintel over the new opening to replace the existing.
(allowing 150mm over hang new lintel would be approx 1800mm)

Ideally the new widened opening would not have doors. The opening is through to the dining room which itself has double internal glazed doors through to living room. Does this make any difference ?

I also assume this definitely does not need planning permission ?
Thanks in advance...

 

[^woody^]

You would not need building regs approval for the door widening, but if the wall is supporting joists then you should need approval for that - to ensure that the lintel is adequate

You would not normally need the expense of an engineer as long as the builder uses a suitable standard lintel

This does not need PP

 

[Gotaquestion]

The wall is supporting some of the floor joists for the room above - and I would expect it's also supporting the floor joists for the room above the dining room on the other side of the wall (I can tell for the kitchen side as I can see the joists if I remove one of the downlights).

I have looked at approx costs for buiding notice only - (I presume I could go this route ? ) price seems to be £150 (inc VAT) for work below £2k - am I reading this correctly ?

On top of this I presume I run the risk of the BCO asking for Strucutural engineer to confirm lintel is suitable ?

I then also need electrical work signing off (wall has a 2 gang socket and light switch for kitchen which both need re-locating once wall removed) - if so I think I am looking at £105 if the builders electrician is not part of comptentent persons scheme ?

Is that about the sum of it - factor on 50% on top of builders estimate for check and tick in the box for building regs ?