I have recently used "blackcircles.com" and had no problems.
You go to their site and input the tyre size that your looking for or enter your registration number and it will automatically pick the standard tyres for that vehicle.
Select tyres fitted or just to supply.
Enter your postcode
Then let the site search for your tyres and prices.
You'll be presented with a range of options which you can filter or just browse through them all.
Pick your tyres and put them into your basket.
When you go to your basket and assuming that you've picked fully fitted, you will be presented with a list of fitting centres near you and available dates, a.m. or p.m. fitting times.
You take your pick on your favourite one.
You'll then be asked to enter your details, and payment details. Usual payment options, credit card etc, and including Paypal.
Once paid you'll recieve a confirmation email.
You'll also get a mail so that you can access "your account" with them.
When you get closer to your chosen fitting day, approx. 24-48 hours according to the site, you'll get a mail with the details again and it will also include a time.
So although you specified a.m. or p.m. the garage have booked you in for a specific time. I don't know if thats a god thing or bad thing but that's how they done it with me.
In the mail they state -"In some cases a fitting time has been allocated to you"
If the time wasn't suitable I would guess you could be able to alter it, perhaps direct with the garage (?)
In my case the mail arrived about 5 days before my planned fitting day, with an acceptable time, had asked for a.m. and got 11:00 timing, so no worries.
It was just a small independant garage I picked so they would not have the manpower/machinery available if everyone turned up at the same time.
I left the car with them for just over an hour (I'm just around the corner from them), went back and collected with no problems, ready and waiting for me.
The price I paid on the site included almost everything and didn't have to pay anything to the garage. The usual stuff, tyre disposal, valve, balance.
I said almost everything.....they do state that the fitted price is for standard valves (for instance), if you've got a metal valve body and wish it replaced then that could be extra.
My experience with blackcircles has been positive so would recommend them.