Downloading new software

You won't know until you download. Garmin has preview maps for North America, but they apparently don't have them for Europe.

You didn't explain why you were installing England, but if you're taking a trip over there the MicroSD card is a better option than a one time download. With the MicroSD card, after your vacation is done you can sell the map on ebay and recoup a great deal of the cost. This is because the map is locked to the MicroSD card, not the device.

I'd also do as Strephon suggests if planning a trip to the UK (switch from Download to microSD version):
https://buy.garmin.com/en-US/US/maps/on-the-road-maps/city-n...

Here's one on ebay right now although it looks like the seller would need to be asked if they'd ship to Canada, assuming that that's where your Kinsgton is:
http://www.ebay.com/itm/Garmin-City-Navigator-UK-and-Ireland...

More on the optional choices:
https://support.garmin.com/support/searchSupport/case.faces?caseId={16315fb0-39b2-11de-5dd5-000000000000}

There are free map alternatives to try.

http://garmin.openstreetmap.nl/

I am going to London in several weeks and have loaded on my Garmin 1490 Garmin City Navigator Europe NT 2013.10 on it. I used it to traverse Ireland and found it very accurate except when I having uploaded a POI found that the Book of Kells was in the middle of a cow field. My mistake, check your POI's.
I do not upgrade my European maps for it will not change for historical sites do not move.
I have 130 plus POI's of the London area on my Garmin and if there is enough requests I will upload it to this site.

Mapfactor has a wide range of free maps for most places in the world.

Don't know how they are for loading custom POI.

You can add custom pois to MapFactor. A little different then Garmin though but not difficult.

The sd Europe was great on our vacation. Could not tell it was on the sd card.
Had all the roads and the pois I needed.
I saved extra pois before I went and they worked great.
With my old unit (750) I made the mistake of buying the CD. It can now be used only with the 750, but the SD car can be used with other unit. It is not updatable but I only need it ever year or so for vacations and I that should be ok. I did buy it new from ebay for $25. This was a great bargan. I got the number off the item on ebay and went to Garmin and checked that it was usable on the 2450 before I bought it.
All was great with the SD card for Europe.