@Gary - With regards to alternative white paints, there is no straight simple answer as it depends on the requirements. As a few examples...
- If we want a tough washable white matt finish, then we still use LG 'Shirting', however we will often base out the walls in a cheaper more economical paint first. Our favorite for this is Glidden's Trade Matt (Which is now re-branded as Amstead in the UK after a recent change of ownership), then apply 2 coats of LG Intelligent matt. (Should note that Glidden's/Amstead is also the paint we use for priming new plaster or as a base coat for strong colour changes). Yes it is extra cost in labour and far from ideal but we still want the tough finish.
- If washability is not so much of a factor or we are painting a ceiling for example, then we use Mylands Marble matt in Pure White which has brilliant coverage.
In your case where the walls are already white, I would suggest touching up the marks with any white emulsion (the left over Dulux if you still have it), then apply 2 full coats of LG Intelligent.
These days almost all paint brands offer a tough washable paint... Dulux Diamond Matt, Crown Clean Extreme, Johnstones Endura, Johnstones Durable, Albany Durable, Mylands Marble Matt the list goes on....However almost all of them have a flaw in one area or another, either with a plastic type finish with Dulux Diamond or others which aren't quite as tough as they make out and suffer from 'polishing' of the surface which shows where it's been washed.
Of course many will see the high cost of 'Designer' paints and assume you are paying for a 'Name' and in some cases you can be. We believe that isn't the case with Little Greene where the extra expense is worth paying for.
When it comes to decorating, labour is almost always the most expensive element, so as professionals we want to be in and out with the minimum of fuss and leave the client with paint finish that will last many years. Many cheap DIY shed paints have issues with opacity where 3 coats are needed as opposed to the standard 2, others such as some Dulux emulsions can react to plastics and form lumps in the paint. Why Dulux choose to sell their paints in plastic containers is anyones guess! and the problem is compounded when most paints are poured in to plastic skuttles/trays/kettles before applying to the walls. So any small saving made by purchasing cheap paints becomes insignificant with the extra cost involved with applying extra coats or stopping to pick hard lumps off the walls when rolling.
Of course if washability isn't a major factor to you then most brands will do a standard vinyl matt, Crown and Johnstones being maybe the favorites with professional decorators, offering a good balance between cost and quality. But even then buyer beware! Tinting machines can be funny old beasts, you can buy the same 'colour' from 2 different stores and have them turn out as 2 completely different colours when applied. Furthermore the colour can change in the same store from week to week depending on when the machine was calibrated, so ensure you buy enough paint to complete your project rather than buying as and when you need it.
Many of the 'Designer' Brands such as LG, F&B, Zoffany, Designers Guild, Paint & Paint Library... Make their paints in large batches with quality controls in place to ensure the colour is the same from tin to tin, month to month.
As explained earlier, one of the most important aspects to us is consistent results. We want the paint to behave exactly as expected, colours to be the same every time and we want to know it will last whilst looking beautiful. If we have to pay an extra £30-£40 per room to achieve that, then to us it's a no brainer!
Sorry I could bore you all day long with the benefits of one brand over another, I'll stop now!
Q