Rolls up sleeves
There are multiple channels in the 5Ghz spectrum. Some are usable and some are usable under certain conditions.
Without going "all numbers" on you;
Band A (lower) is the indoor part, lower end channels 36-48 (5180-5240), max transmit power of 200mw (23dB eirp)
Band A (middle) is a meh which you probably don't need to know about / use channels 52-64 (5260-5280) which is indoors with DFS
Band B is the indoor/outdoor where by you MUST use DFS regardless if you are indoors or out channels 100-140 (5500-5700), max transmit power of 1W (30dB eirp)
Band C is outdoor and designed for PtP and you should be using an OFCOM license for, channels 149-161 with a max transmit power of 4W (36dB eirp)
Point to note ^^ Band C has just had some changes where there are now 6 usable channels not 4 but I don't have the channel numbers to hand but regardless you shouldn't really be using them.
So...
Stick with band A for home use, it's indoors and believe me power really isn't everything although the uneducated will often argue this.
There are 4 20Mhz channels in band A, 36, 40, 44 and 48.
If you use a 40Mhz channel width then there are 2 channels available (2x20Mhz's make your 40Mhz)
As you'd expect 4x20Mhz channels would give a total of 80Mhz width which is where your 80Mhz channel comes from.
The channel "number" in this instance is more dependant on your kit, for 40Mhz some use Ce (Channel & Extension) and some uses eC (Extension & Channel).
80Mhz gives more variation of this, your channel 44 with 80Mhz consists of eeCe (Extension, Extension, Channel, Extension) if we are operating in the previously mentioned Band A.
The wider the channel the faster it will go however the density of your power decreases by 3dB as you double your channel width (20>40>80).
Imagine it's like using one of those small pots of jam on 1 slice of bread, 2 slices or 4 slices. The jam is your power (23dB) and the slices are your channel widths (each at 20Mhz). 1 slice the jam is very concentrated, double the amount of slices and you half the amount of jam per slice and then halved again when you double the slices again. Easy way to remember is +3dB is a double in power and -3dB is a half in power. Bear in mind though the power from your router is not reduced at this, you are just spreading the power more thinly across the spectrum.
TL;DR
Stick with 80Mhz on channel 44 as some devices may support it and most routers will drop down to 40Mhz to cater for non compliant devices. On my access networks I operate 2.4Ghz on 20Mhz width and 5Ghz on a 40Mhz width as not enough 5Ghz stuff supports 80Mhz yet and you just increase the collision zone.
Otherwise make sure your router is set to UK locality with an up to date firmware and trust it will operate legally for you and within the parameters set by OFCOM.
Your address says London which from my "small town" mentality makes me think of densely packed areas with lots of local noise so you'd be better operating on slimmer channels and actually reducing power if you can to reduce the noise floor to get better signal to noise.
Thanks, you know your stuff, they should put your info into a sticky.