I checked my hive the other day and already clocked this - second time I have clocked forage issues before the NBU sent out emails - my only concern was that I don’t want sugar syrup in my honey so how much is enough?? Thoughts??..
http://us2.campaign-archive2.com/?u=1b3026ffe9de637a5feece3be&id=22ab6a0e29&e=34c56abb5e
Hard to answer that, @Valli. In my area, generally people like to leave the bees around 40 lb (18 kg) of honey going into winter. That would be approximately a full medium Langstroth box. However, it is not the beginning of winter. Also, it seems that they are concerned about the Northern UK, I would say that you are more Midlands. I would think that if your colony has 5 or 6 full deep Lang frames of food, they are not short and I wouldn’t feed them. Maybe some UK beekeepers on this forum will have more directly useful advice.
40lb is the gold standard here in the UK
Some of my colonies had less this last winter, which was mild with the bees flying most weeks, I still had to pull a frame or two of stores on first inspection.
In between inspections once the season is underway, a frame’s worth of food,nectar, is enough to last till the next one in a week even if the bees can’t get out to forage.
Pollen is not so critical. The bees need as much as they can get but if there is a dearth they will simply stop brooding.
Our NBU trot this sort of stuff out two or three times a year well after most beekeepers have discovered this themselves.
They did have a couple of frames at the beginning of April - They have eaten it all - there is only some pollen and brood on the frames - twice as many bees as beginning of April but they have eaten the stores they had. And we are expecting a cold blast again this week into the weekend.
I’ve given my bees 1lt each of 3:2 Sugar syrup today - it was 15°C and quite mild here today but there is the cold blast coming. We had snow last Saturday. It was wet and melted pretty much straight away.
Some years we have heat waves - British weather is very unpredictable. the last couple of weeks we have had April showers I was away for a week up North so not sure what here was like
I saw another bumble bee a small solitary bee and my girls out foraging in the garden today
Villi,
Our normal around here in Puget Sound/Seattle region into the Cascade Foothill a full 10 frame deep Langstroth body. It’s not that we are extremely cold but a long period without pollen crops here. So my new bees seem to 
off to a fair start. Lost out on first half of the local huge Big Leaf Maple bloom here. We will have a lot of small waves of pollen but our next huge pollen surge will be the introduced n very invasive European blackberry crop … They grow n bloom like crazy along freeways, edges of fields n forest n anywhere else they can get their roots into.
So hoping my girls can come close to that with having to draw out comb then store needed winter supplies of honey n pollens. About 80 pounds I’m told. As a kid … I remember the winter deeps were heavy even for a young muscular teen kids ! 
Take care. Gerald.
G’day @Gerald_Nickel - the Rape is in bloom here but the weather has not been consistent for the bees to be out - My girls are too far from it anyway - I have Bluebells, Grape hyacinth, The Cherries locally are still blooming - probably because the bees have not been able to get to them, Verbena’s, Mahonia, The daisy’s and Dandelions in the lawn, Pulmonaria, Green Alkanet. I saw a neighbour has Forget-me-nots out, Rosemary, Broom, just a few close in the backyard and adjacent neighbours - the plants are there, it is the weather not playing ball.
Villi … I see a lot of dandelion but too much Maple at present to interest them. My for-get-me-nots are blooming here too. I am guessing our climates are similar ! Most of your list … Would be my list too ! We don’t have the rape weed locally. We’ve gotten a break a couple times last few weeks but just came out of the Wettest Fall/Winter/Early Spring in our recorded Seattle/West Coast history. About 24" we are currently 5-1/4" above our norms yet. That’s why my Nuc’s came a dab late. There are having a hay-dandy-time now but cooler n damper weather in the forecast for the next few days again. That forecast like yours can change. Yours off the Atlantic n ours off the Pacific.
Our hardy welsh bees are out and about even at 7˚
I have two or three frames of fresh nectar in the brood box of each colony when I looked yesterday.
The Buckies are still munching winter stores but 5/6 frames solid with brood so looking good