Based on how the volume limitation works, and also based on checking my own A105 after the last firmware update, the limitation is not removed. Honestly, I'm not sure they're gonna remove the limit just for UK so soon, or maybe they'll never do it. They would have to change some basic stuff about the firmware, which I just don't see Sony doing on already released players.
I would say that NW-A55 would be a better deal, as it has a line-out output (using a special and very cheap cable), which sounds better than what comes out of the 3.5 port (as you mentioned using it with a Hi-Fi amp). You also get a BT Receiver function, to stream audio from a device to the A55 via BT, and also a USB DAC mode, functions which are not available on the A105.
A55 is the same size as the A105, but it doesn't run Android, the battery lasts longer, and it's cheaper than the A105. You also have the possibility to install custom firmware which can improve the sound quality, and you can also remove the volume limitation for EU devices.