You’ll have a choice between a 700c and 26" wheeled bike.
26" wheeled are stronger, heavier, more agile, generally lower geared. They’re based on mountain bikes.
700c wheeled bikes are weaker, lighter, more stable, generally higher geared. They’re based on or pure road bikes.
You get what you pay for to an extent. For a 34 mile day 5 times a week, I’d be looking at no less than £700 RRP really. You can buy a cheaper bike, sure, and it should work. But it’s a bit like buying a kymco 125 for the commute. Unless your commute involves riding in the woods, suspension is extra weight and less efficiency. You don’t want it for the road.
Suitable bikes are split into about three groups:
Road bikes, which are similar to the bikes raced, have 700c wheels. They’re the bicycle equivalent of a sportsbike. They’re comfortable when you’re used to them, but not when you’re new to them. There’s not a lot in the way of carrying capacity, and they want looking after. They start at £500, a ‘decent’ one is £1500+.
Examples are Specialized Allez, Trek 1000 series, Cannondale R series.
These can be subdivided further into flat-bar road bikes, which are essentially the same as the above, but rather than having racing-friendly drop handlebars, you have normal-person-friendly flat bars. Some manufacturers make only this change (Trek, Genesis), others create a new line of slightly tougher road bikes (Specialized Sirrus, Marin do some, too). Same prices as road bikes, same componentry.
Touring bikes kind of fit in here, too, but they’re also a bit like hybrids. They’re essentially the BMW GSs of the bicycle world (with absolutely none of the attached fashion, quite the opposite). Essentially toughened road bikes, they need to be got used to and do involve carrying some weight around. Good ones last forever, though (Dawes, Thorn, Roberts).
Hybrids, which again split into two. One lot are the flat-bar-sort-of-road-bikes mentioned above, the other group are what most people think of when they say a hybrid. They’re 700c-wheeled, with a beginner-friendly sitting position. They’re the CB500, ER-5, GS500, Gladius of the bicycle world. Generally quite heavy, almost lumbering, strong, dependable and entirely unexciting.
Examples include Specialized Globe; Marin Point Reyes, Belvedere and San Rafael; Trek F series.
The last are basically mountain bikes with slick tyres on. They’re the supermotos. Fast, nimble, agile, quite fun, able to carry stuff, but not particularly gracefully. Very durable, not ideally geared for long rides, but pretty good for knobbing about in traffic. Start at £300 as with MtBs, get good £500+.
Examples include Cannondale Bad Boy, Ridgeback Storm, Marin Point Reyes.
Assuming you’re riding it as you said above, quite regularly:
Tyres are about £40/pair and you’ll likely need at least two or three pairs a year.
You’ll also probably munch through a chain and cassette at least annually, at about £50 a pop. You’ll probably need chainrings after two or three years at ~£50+ for the set.
You can get through three or four sets of brake pads in a winter, at £5-£10 an end. Two pairs should do the rest of the year.
Servicing you’re probably looking in the region of £150-£200 for an annual service, including the abovementioned chain and cassette if you time it right.
Labour costs in London is around £40/hour.
Bicycles are nowhere near maintenance free.