Here is the O2 (UK) 4.4 Kit Kat with Sense 5.5 RUU version 126.96.36.199
It has radio version 4A.23.3263.28 and will work with this config:
File name is:
RUU M7 UL K44 SENSE55 MR O2 UK 188.8.131.52 Radio 4A.23.3263.28 10.38r.1157.04L Release 353143 Signed 2
You should not need to downgrade your hboot version for this RUU to work. This should work for most S-On users that need to return to stock since there a lot are on a software/hardware versions lower than it.
If you need support for using this file you can use this XDA thread:
The full list of RUU files can be found here: