the palms - probably not. Yep, some palms will survive outside, especially in the south of the UK - I am thinking of the obvious trachycarpus fortuneii and chaemerops humilis....and also, the phoenix canariensis date palm will be OK once a certain size has been reached (around 4-5 years old)....and the jelly palms - butia capitata - are proving to have surprising hardiness.

Rather than bringing them inside though, you might find the palms do better outside with extra protection. Raise the pots off the ground on bricks, wrap the pots with bubblewrap or sacking and wrap the white horticultural fleece around the top part of the palms - I tie the fronds together with a strip of fleece first.
I looked after a customer's large phoenix palm until it was around 8-9 years - it was starting to make an extended trunk instead of just a huge round base.....but idiot customer kept hacking away at overhanging fronds - let a virus into the wounds and the whole thing died horribly.

Not sure which iris you mean....but as a rule, they are generally hardy and require no pampering.

The date palm is likely the "pygmy date palm" which is smaller and less hardy.

I am in 8b and I have kept a sago palm outside for 12 years in the ground.. My winters are different from yours. I have not had a frost yet and our frost stick around only briefly and we are back to pleasant temperatures. We also do not get as much moisture as you. I protect the growth point when I get a BAD freeze (one below 20) with a towel and if the palm is still small , a moving blanket thrown over it. Mine is too big now for the blanket. I find that the fronds die back if it gets cold like that, so I cut them off before the freeze and pile them up against the trunk and cover the center growth point with a blanket. The palm replaces all of the fronds in the spring. It is 6' diameter plant now. It got to 12F(-10.5C) a couple of years ago and 16F(-9) last year , My mother in law had been growing hers unprotected for 30 yrs, but she is in the Urban heat dome of Austin texas, and is a bit warmer. Hers was always in a pot. It got to be a really BIG pot.
Here is a excerpt from Geof Steins article on DG. You can read the rest of a good article there, Tittled Sago "palm" care and cultivation, but I can't list the site here. Against the rules.

"Care of Plants in the ground

In many climates throughout the southern US Cycas revolutas can be grown in the ground. Well draining soil is recommended, but these plants are fairly tolerant of clay soils as well and seem to adapt pretty well to many different soil types. Temperatures below 15F briefly can be damaging to the leaves, and below 10F to the stem as well. If exposed to such low temps for longer periods of time, the stem may be permanently damaged. Temperatures over 110F for a long period can damage the stem as well, and hot, dry sun exposure will sunburn the leaves (making them unsightly, but will do little damage to the health of the plant). "

This post was edited by wantonamara on Sun, Nov 9, 14 at 14:40

mushibu10, Sago Palm (Cycas revoluta - not a palm at all, in fact) is only hardy in the mildest of UK climates and then not reliably so. In Wiltshire I'm pretty sure it will not survive the winter outside. If the date palm is just one grown from a date seed it will not be hardy but if it is, as Campanula suggests, Phoenix canariensis it may well be OK, especially if you give it a fleece covering.

Campanula, why lift the palm off the ground on bricks? I would have thought that contact with the ground would keep the pot warmer.
MBWD

Winter wet is often more of a killer than cold....so just adding the extra drainage facility of raising a pot off the ground, allowing a quick flow of water through drainage holes is helpful....This is really noticeable in stone or hypertufa pots, with my collection of alpines. Conversely, you could raise a glass cover over the top of the pots to protect from winter rains.
Maintaining contact with the ground may well make a difference to heat retention....but at least here in the UK, the differences are too small to measure.....although I do have a friend who assiduously plunges her pots into a sand bed for winter.

Campanula, What you say makes sense if I understand winter weather in the UK. In North Carolina, we have many warm, sunny days in winter, followed by extreme cold. And the temperature swings between day and night may be extreme. So often the ground is much warmer at night than the air. Here it makes some sense to maintain contact between pot and ground and in-ground plantings can handle cold weather much better than their pot- bound siblings.

But my expectation is that the UK has more even temperatures in winter with less day/night variation and more cloudy weather which prevents wild temperature swings. That combined with frequent winter rains could make drainage the priority. Does that sound right?
MBWD

Plants in pots may be as much as 20 degrees F. less hardy than the same kinds established in the ground. I would not leave any of the plants asked about in the original post out in frost.

The first part to go is the new roots on or near pot walls. Older roots back inside as well as the tops of the plants are hardier. Therefore, after significant cold exposure it can appear plants have not been damaged when in fact if they were taken out of the pots it would be discovered that about half the root system was dead.

As long as we keep a westerly wind I believe it's a warm winter (still have frost) but depending on the easterly we may have a cold white winter at times but still very cold.
Our temps are more stable throughout the winter but it may stay minus 5 for days/weeks I believe.

I'll bring them in ;too much hassle.

Floral_uk I have herd people sinking pots in sand too. And covering alpines with glass just to keep dry.
Thank you

'....it may stay minus 5 for days/weeks I believe...' No it won't Mushibu. -5 is rare and never prolonged. I don't know where you are in Wiltshire but in Swindon the coldest month is February and the average MINIMUM temperature is 1.1. (33.98f) The average MAX is 6.8.(44.24) So the range is indeed not huge.

The pot sinking story was Campanula's, not mine.