I supervise the distribution of Yellow Pages over several areas. Until recently (when we started using computerised maps), Philip's Street Atlases were the standard reference work for my job. (Which meant that I got them paid for!).
The reason why we used them was because, unlike street maps produced by other companies, there are NO GAPS in the mapping. Their Berkshire volume will cover EVERY street in the county (and quite a few just beyond the county boundary as well).
Google confirms that Mortimer and Burghfield Common are definitely both in Berkshire, so you can be confident that they'll be mapped within Philip's Street Atlas of Berkshire.
Chris