Thanks Tim I will have a look next time I get the chance and report back

I've heard back from UK AIS. They confirm the height of both obstacles has been corrected to around 150 feet, which is why they're not appearing in SkyDemon. They also told me they'll be removed from the next printed 1:500k NATS chart.

I can see the two you mean. Their height means they would be included in SkyDemon charts, which means they have probably simply been withdrawn since the issue of the printed chart you're comparing with. I will ask the UK AIS to confirm this, but that is in all likelihood the explanation.

The towers I reported on the half mil chart are 790(397), immediately north of Brighton Marina and 1080(525) on the eastern outskirts of Hastings using the nomenclature of the CAA chart

We display all obstacles that are published in ENR 5.4. These tend to be obstacles of 300ft height or greater. The NATS 1:500k chart shows more low-level obstacles, but we do not intend to add those (less than 300 feet high) to our chart. Can you confirm if the two you're referring to match that description?

I have noticed two obstacles on the CAA charts which are missing from the SkyDemon charts and I wonder if there are any other reports so that we can improve this important information
A tower is missing just North of Brighton Marina 790 feet amsl
A tower is missing on the eastern fringe of Hastings 1080 amsl, this used to be on Skydemon but it has gone awol