Caradon Hill is a Group A transmitter. That means that all the frequencies it transmits are in the lower half of the frequency band, and that's where the majority of the aerials at
Screwfix don't work that well. [Conclusion 1 -
Screwfix isn't the best place to buy an aerial for your local transmitter]
Of the aerials at
Screwfix that might be suitable (the Log Periodics), the closest they have is a short-ish length Log with a 16dB amp (Labgear 27885LAB) but (a) it's shorter than a conventional Log Periodic so won't pull in as much signal before amplification, and (b) if you're as close to Caradon and with good line of sight as you say then you definitely don't need a masthead amp, so that aerial begins to look very expensive for your needs [Conclusion 2 -
Screwfix isn't the cheapest place to buy an aerial for your local transmitter because their selection is limited]
Outdoor chimney mount is my preference but I wouldn't buy/use the type of bracket that
Screwfix sells. I've been to enough installs to replace this kind of bracket along with the aerial. The problem is they're small and they don't spread the load over a big enough area and so overtime they move with wind pressure on the aerial and wreck the pointing. Ergo: cheap bracket that destroys brickwork and causes hundreds of £££'s worth of water damage isn't a good buy. Their wall fixing kit is one of the cheapest it's possible to buy as well. There's not enough length on the arms to clear most eves, so it will end up fixed to the soffit which isn't that strong a place to fix to for something that undergoes a bit of wind loading. The U bolts look weedy too. The result is that you'll overtighten the U bolts to compensate and so crush their thin alloy 1.8 mtr mast in the process. Sooner or later that mast will bend and snap. [Conclusion 3 -
Screwfix's bracket range will end up costing you dear in remedial work and replacements]
Other observations:
(1) Most of their aerials are mis-described - There's no 19 or 48 element aerials on that site, they're counting elements twice or four times to come up with those numbers. It is the equivalent of saying you drive a ten wheeled car because there are four rims + 4 tyres on the road plus a rim and a tyre in the boot. Utterly ridiculous
(2) Next, those aerials such as the Labgear TV Aerial High Gain 48-Element aren't suitable for outdoor use. The reflector (the big rectangular section at the back) has no support between the fins. Birds will land on it and bend them partly because they're not supported by the neighbouring fins and partly because they're made of very thin bent bits of aluminium for cheapness so they're not that strong. Again it's a case of buy cheap, buy twice
(3)
Screwfix aerial and satellite cable is crap. The best they have is Labgear PF100 which uses aluminium plasti-foil and a relatively weak outer jacket. What happens is that the jacket cracks due to weathering and then water gets in to the cable. There's a reaction between the copper and aluminium that then eats both. The result is a worsening signal until the point where it goes completely because the electrial earthing circuit breaks down. You'll then go nuts trying to work out why there's no telly picture, she'll be nagging you, and eventually you'll stump up for a whole replacement aerial and cable again (possibly with the same type of cable) when spending an extra £4 on some Webro WF100 would have prevented all that hassle. Oh, don't even bother with RG6, that's really poor stuff.
I use
Screwfix a lot for my electrical supplies and tools, but they're not the best place (or even the right place) to buy aerials and associated ancillaries. They sell gear to electricians who think "aerials is easy money" or "how hard can it be?" but the gear they sell is poorly specified and there's no advice in store to help the hapless trade or DIYer when it all goes wrong.
If I was in your shoes I would buy a
Vision V10-036 Log Periodic aerial, an
8" galvanised lashing cradle, a lashing kit, a 6ft 1.25" (32mm diameter) alloy mast, an F connector (for cable to aerial joint), a Belling-Lee TV aerial plug (from cable to TV), and some WF100 coax cable plus any cable clips you might need. My bet is that being so close to the transmitter and with such good line of sight that you'll get a tonne of signal with just this simple and inexpensive set up, and it'll last years too.
Loft mounting - Yes, it can be done (use the same aerial as above) but you'll have to spend a lot more time testing the various places in the loft to get good signal. It's not always where you think is obvious. Also be prepared to spend some time rejigging the install if you lose signal in the rain.