It's huge, the one at the back in the middle. I'm based on the UK.
Impossible to be sure what it is without close up of leaves, but I'm thinking maybe Poplar from the growth habit. Either way, the only safe way to have this removed is to call a Tree Surgeon (known as an Arborist in the USA) preferably two different ones, and get a couple of quotations for the job; you can find one in the Yellow Pages, Thompson directory or simply Google 'tree surgeon' for your area of the UK. If you don't want regrowth, either ask for the stumps to be ground out, or for them to treat the stumps so they don't regrow; check with both tree surgeons that their quotes include for taking away all wood and debris. If they're proper tree surgeons, they should be able to identify the tree easily.
UPDATE: The close up pic of a leaf you posted shows a slightly spiralled gall at the base of the leaf, where it joins the petiole; that, coupled with the shape of the leaf overall, makes me pretty sure its a Poplar, one of the Populus nigra varieties such as 'betulifolia' or Populus nigra 'Italica', which is much more fastigiate (narrow). If the bole or trunk is burred, that would confirm this ID. Average mature height around 35 metres.
The gall at the base of the leaf is caused by a particular aphid (pemphigus bursarinus) which often infests Populus nigra varieties here in the UK. The advice given initially regarding removal of this tree remains the same.
It is very hard to tell what type of tree it is. Can you get a few close up shots of the bark and/or leaves for us.
The best recommendation to remove trees is to get professional help. I don't know what stands around this tree in terms of other vegetation, property, power lines etc., but this is probably not a DIY situation if you are not an arborist yourself. You should be able to look up local directories etc. and seek out a good service.
Then, you could tell us what their recommendations for removal are, and we may be able to provide much more relevant feedback at that point.
Update: This is most like Basal Poplar(Populus balsamifera). Take a look here:
You could post it online or in newspapers that you are giving a way free tree. You would be surprised by how many people will respond. Be very specific and provide as much details so that you minimize inquiries.
We did this twice and both times trees were successfully removed for free. One time tree was so big that we got local news involved and they made buzz about removing a huge tree in community. This help us get professional tree removal company, electrical company and a roll off dumpster company. They all volunteer for the exposure and contributed to the local community. I don't remember the electricians as they were out of state doing a project in our area but landscaping company was LandworkContractors and roll off was Easy Dumpster Rental. I can look up the electric company if anyone is interested but you are in UK and I doubt these companies will go there - haha.
A 1-2 person job while being safe:
Have your kid climb (I did this as a kid, and it was FUN!!!) as high as they can cut with clippers
have the kid clip off most of the limbs as far down as they can get
Climb as high as you can with a saws all, and start cutting
repeat until it gets as low as you want to cut it/can
break out the chainsaw
fall the remaining parts of the tree