Not quite pocket-sized, but no bigger than most modern field guides, this might well be the standard illustrated guide for amateurs to the British and Irish flowering plant flora. The guide covers all naturally occurring species plus a large number of naturalised plants. As pointed out below, botanical experience will make the use of the book easier, since there is no general key allowing the user to identify families. However, I wonder how many beginners would really be prepared to spend the time passing each new plant through such a key. For those who can roughly identify a new plant to family and beyond, handy keys ARE provided for the larger groups.
The format is very similar to the "Wild Flowers of Britain and Northern Europe" by the same authors, published by Collins. However, all the illustrations are new and improved. The previous guide's plates were often blurred or otherwise lacking in definition, a problem that does not occur here. A further improvement is the provision of maps that are small enough not to include for the majority of species yet large enough to allow for a fair amount of detail.
The section on grasses is new and particularly useful, truly enabling the user to identify all the flowering plants in the region.
The only other competitor would be Rose's "Wildflower Key" which I have in a 1981 edition, having not seen the current 2006 issue. All in all, the present guide is superior.