The dates are only a guide not a rule. Not only do conditions vary from north to south but from year to year. Obviously its reasonable to assume Bristol is milder than Inverness but we have to temper the guidance with our own judgement.
It depends what you are sowing too - to be on the safe side I would leave your beans until May or at least late April as the packet suggests. Obviously its reasonable to assume Bristol is milder than Inverness but though some of the days are getting milder the nights are still pretty chilly. The state of your soil is also a factor- if its too wet and heavy wait until its dried out and warmed up a bit. If its too cold and damp your bean seeds may rot rather than germinate.

If you are in a hurry you can always start some off in pots under glass or under a cloche run, but leave the cloche in place for a few days to allow the soil to warm up first..you could even hurry it along with a sheet of black polythene in there.

Lacking a climate map, and a series of planting dates, such as some companies here in the States do, I would look up where the company is based--sowing dates are likely to be best for their location, and can be adjusted according to how your climate differs from theirs. I wish that there was a consistent, quantifiable system for exact description of climates--or that there was one that didn't require a masters degree to understand! :)

I once read of a farmer who judged the right soil temperature to sow his wheat by pushing his trousers down and sitting on the land in his bare bottom.

I think Stera. has given you some clear and sensible advice re sowing seeds. Oddly enough sowing bean seeds in Inverness late April would be pretty common up here, Aberdeen would be a whole different ball game! It is always better to wait an extra week or so rather than start them too early and have a frost, or cold wet weather hit. Our soil in Moray is warming up but wouldn't plant any veg seeds yet.

Just to add, it's always better to sow late as the plant grows away quicker and probably ends up a stronger plant as there are no checks in its growth so later sometimes ends up earlier.

Agree Jimmy

Probably good advice for moderately cool climates, like most of the UK. In areas with very short growing seasons, such as Scandinavia, with its long winters, or here or parts of Australia, South Africa, or India, with our extreme summers, we have to be pretty on the spot. Otherwise our crops freeze or burn!

Well the possibility of freezing is alway with us but not burning Tugb.

lol! True, MG! Some cool-season crops probably are in danger of bolting, though, especially in the south.
Here in the desert, we have to plant our tomatoes out before the last frost, and plant short-day onions, or we wind up with stewed tomatoes and grilled onions in the field! :)

I have always said gardening is a science subject which should be taught in individual school programmes.
Even generalised Botany does not apply to every district.
These comments prove I am right.
Every district is different weatherwise and geology wise.
Teaching it in schools would create more interest for
children. All this taking notes from Monty and Co
on national T/V is wrong.

Trouble is Diane it doesn't fit into the national curriculum. Up here at least most schools have a gardening club which helps children to understand, problem is their parents need educating first as few of them grow anything from seed - never mind veg.! Don't get me started on the GC's who have annuals for sale up here in early March knowing fine well they can't be planted out until end of May early June.

My private flat is part of a block on a council estate. I bought it because the price was right. It was a good buy.
Tenants always moving out, have been for years.
Its very hard to make them understand ball games are not allowed. A playing field is available for children just down the road to go and play football. I have told them broken windows cost me £62.
Greenhouse broken class £30 a sheet.
I try to teach them gardening by always enjoying my garden plants, spending lots of time out there, taking part in the council best back garden competition.
Talking to the children about plants and where they come from. Its an uphill job.
You are right about the parents. All they think of is to have more children so more than 2 of different sexes are overcrowded legally, so they can get a house ........all for free !

Thank you to everyone for your comments. I asked because I remembered a discussion on QI (TV show) which referred to the appearance of daffodils in spring in the UK, saying that their appearance spreads from south to north, moving at approximately the pace of a person walks, taking six weeks from their first appearance in the South until they reach the north of Scotland. With this six week differential it seemed odd to have one single fixed date on seeds with no reference to area.
I take the point that owing later will often bring better results, but I prefer the idea of staggering my sowing in order to get a longer harvest time.

Staggering sowing is always a good idea... and whilst bulbs may flower 6 weeks later in the north of Scotland than they do in the south of England the weather at both ends of the country is all to pot right now! Most of our spring bulbs have flowered and are going over and this is mid April, next year it could be late April before we even see a flower! Not I am talking about bulbs not perennial plants.