This is ridiculous!

[#1]

Yes I was setting up new router but it was not working wirelessly so I connected the old one. That is probably the reason.
The problem I have is that I am not receiving 1 Megabyte, I'm only getting 500 Kilobytes despite my line being 18 Megabits.

[#2]

I've just realised that it could be related to my computer.
My laptop receives 18 Megabits today but my computer is only receiving 4 Megabits. What could be the issue? Driver related?
I'm receiving my internet speed that I had previously

[#3]

Are both your laptop and computer connected via wireless and what speeds do you see if they are wired?

[#4]

FOUND THE PROBLEM! I've got 2.1 Megabytes download speed. Finally!
My Killer ethernet port limited bandwidth which meant I received 500 Kilobytes. Therefore the engineer may not have been necessary but the disconnections were fixed!
My computer was the problem by the looks of it. I don't need the engineer to come out now. Thank you all for the support, been great!

[#5]

Hi,
Can you please clarify the last statement please?  Modem stats are always very useful as a datum in these discussions when the speed results are different.
Is the PC wired or wifi connected?  If wifi what standard is that a / b / g / n / ac ?
Similar for the Laptop.

I think we need very clear / precise descriptions of your concerns to help you here... "I am getting 18Mpbs BTw speed test on my laptop when wired connected to the router, however on my PC wifi connected using software ABC to down load files from xyz.com only works at 1 megabyte / sec when downloading a 100MB file".
There are a number of potential culprits for DATA transfer speeds being not what you are hoping for.  Usually (especially if you've had issues) the problem is line / synch rate.  Your problem (BTw data speed on being 4Mbps) was looking like a profile issue, given what you've just posted, I am starting to think that other factors need to be considered.
WiFi version speed variability
Machine performance
Software tool operation

As a point of reference, doing the same things the same way on each of your PC and the laptop will be an informative comparator.

Edit ... hmm seems like you followed the logic whilst I was typing!    It is a good illustration of how end user equipment can contribute to expectations not being fulfilled in less than obvious ways!