You have to order it from the Dell UK website. If this is the laptop I think it is, it's VERY good (the Dell Inspiron 1545) because I have the Dell Inspiron 1525 and it's great! Dell are usually very good with deliveries though, mine came within five days of my order being placed. Dell should give you an expected arrival date but the laptop will almost certainly arrive before the date that they give you.
BTW, if you didn't know, you have to configure the laptop with whatever specifications that you want. I hope that helped.
Edit: If you click on this link, this is the Dell UK page which is all about the Dell Inspiron 1545 will appear. At the moment, there is a deal on this laptop, but only until the 22nd of July.
Link