House is just too cold

Get yourself a heated blanket throw for each family member for now... they are super cheap to run and you won't waste money trying to heat a house that is obviously badly insulated, as many houses in the UK are. It's national scandal if you ask me. Get someone in to look at what the problems are. Tackle them in the summer months when such things as insulation are cheaper to buy. (edited)

Buy a thermal imaging camera from eBay. Check the house for heat loss then sell it back on eBay.
Also check the specs of the radiators. Are they sufficiently sized. Maybe they are undersized for the property. You can check online for the correct radiators needed for each room in terms of kw,btu etc.
Also seal any air gaps.
Check window sealant
Around doors and windows internally and externally.
Around skirting as you mentioned as it may loss heat but can let a cold air draft in.
One of the biggest is plasterboarded walls. As if they haven't been sealed at the top near the roof points or windows they will allow cold draughts to flow behind the boards.
And as above top up insulation as much as you can in lofts and especially below any wood floorboards on the ground floor.

Nice comfy blanket for your legs, we're all doing it. Works.

If not heated for some time the fabric of the building will absorb significant heat before you see any real comfort warmth, especially if there is a limited amount of furniture / furnishings.
The 17C seen by neighbours will be residual from multiple previous heating cycles.
If you want to feel immediate comfort warmth whilst waiting for your CH to do its bit then consider a fan heater or direct-radiation heater such as halogen element.

Maybe it’s haunted.

The house is cold so it's going to take time to warm up.
Heat travels to cold. Soon as you turn off the cold house structure will drain heat. Our house heating is off now at 20c
Will be 14c by morning when heating comes back on.

Go around and look for holes to the outside.
Around pipes ect. Smallest gap can causes major heat loss. I've even taped up key holes.
Check out under bath as often holes there through to cavity.
Floor board? They will leak cold air through gaps.
Gaps under skirting
All the doors and windows sealed?
Consider covering windows with clear plastic and you don't have to use the proper stuff. Cheap stuff will work and tape.
Loft insulation? Put hand under it and will feel warm. Problem is way too many houses lack enough.

I’ve got gaps between skirtings and wall round the house, but not that big that it would cause heat loss?
Next step putting curtains on!
ive for really big windows so don’t think that helps either!!!!

A house made of brick or block acts like a heat sink. It takes a long time for the heat to transfer from the air which is warmed by the radiators into the house structure. Once there it will slowly dissipate over time and will disappear more slowly if the house is well insulated. If a house is stone cold in winter it might take 1-2 days or more with the heating on until the house retains enough heat so that with the heating off the internal temperatures don't drop to what it is outside. I used to have this problem with a house I used one night a week for work. I'd drive up in winter and the central heating would barely put a dent in the cold for a one night stop. If I occasionally stayed a week and left the heating on for 24hrs, after that it was fine to only have the heating on the usual times morning and evening.

if you've just moved in, i suggest get a gas engineer to do a boiler check for safety and ask them to set it at the most efficient settings and balance the rads, and let him know the issues you have and see what they can suggest. then you know the boiler is safe or not or needs work or not, or if the rads need bled

Insulation is absolutely key to retaining your home heat.

You can heat the house with new boiler etc... but if you are heating the street and the sky etc.... its being wasted.

You can in some cases qualify for a grant for insulation.

Check out the roof especially, and also if you can have cavity wall insulation then go for that too.

Floor insulation is also worth looking at - but I would only do this if redoing floors anyway as its a big undertaking.

I can assure you it makes a HUGE difference.

13 degrees isn't too bad tbh if heating hasn't been on and it's in minuses outside.

I generally only have heating on once a week, and inside temperature usually hangs around 13.

If it drops down to single digits I maybe put a fan heater on for half hour or so to warm a room up.

Go outside for 20 mins, the house wont be so cold