There is a RA(T) over Central London listed in the NOTAM for Wed 27 May, in the text it says radius 2.5NM, however when I hold press on the map within the RA(T), it shows 3.0NM in the limits section (see screenshot).

Having also read the NOTAM on the NATS website, nowhere does it say 3.0NM. So why does it on SD?

This is on iPad rMini (iOS 7.1.2.) and latest SD version. Not tried it elsewhere.

The bit you're reading is free text. The actual definition of a NOTAM's effective radius only supports whole numbers, and it's 3nm in that case. Here's the NOTAM's Q line (which defines its coordinate and radius) on the NATS website:
Q) EGTT/QRTCA/IV/BO/AW/000/025/5131N00008W003
The radius is the last part, 003 nm.

Thank you for responding, very informative and enlightening. It just goes to show that even the official source can be inconsistent/confusing too.