Devon,
United Kingdom 
Tried to show a pic of my fatsia japonica but my brain isn't in digital mode today. Most of the leaves are yellowish although some do seem to be the right green colour. It's also on the verge of flowering but I know there is something wrong. Could you advise me even without a pic? It's been in a mostly shaded position for about 4-5 years and the soil is clay. In the past, it shed the bottom leaves but these have now regrown although they too are yellow and I'm afraid that they will drop off. The whole plant looks sickly.
25 Sep, 2017
Answers
It's quite sheltered but we had a tree taken down last winter and the space does get more sun than it did although only a couple of times a day. I expect that's the problem. Thanks for the info Bamboo.
26 Sep, 2017
They usually look like that if they've had too much sun - but they also do not appreciate too much wind. Given that the UK is now much windier than it used to be, could that be the problem, that as it gets bigger, its more exposed?
25 Sep, 2017