Good choice, cycling to work given its that close.
Covers generally don't work for bicycles because they tend to be lightweight and offer little real protection. Your bike is already wet cos you rode it.
Bikes can live outside in the working day, and as long as you store them inside at night deterioration is minimised. A 40 hour working week is still only ~25% of a 168 hour week, so not leaving it outside all the time will help the most.
Things you can do while parking:
- Park your bike in a more-sheltered area. Ideally under a porch roof or carport or something. Second choice would be beside a wall to provide some protection from the prevailing nasty winds (southerlies for me, probably winds from the north/ocean for you ?)
- Avoid parking under trees, if you can. Trees tend to gather moisture and drop it a lot longer. Also leaves and dirt hold moisture.
- Parking in the sunlight and not the shade is helpful if possible - even in the UK.
Things you can do to your bike:
- MUDGUARDS! (fenders) are fantastic and will help keep your drivetrain and you much cleaner. Try to go for full-length ones, not the stubby cosmetic ones.
- Saddle - consider a plastic saddle and not a leather one. Properly protected leather would be okay, but its a hard life for wet leather. A stout plastic bag on the saddle alone can help, but condensation still makes it damp on the inside.
- Brakes and rims - will suffer from road detritus and will wear out faster. Best protection here is to wash your bike periodically. If you feel or hear grinding while braking, its stones or grit abrading your rims and costing you money so wash it clean. Disks are slightly better here.
- Lock - given your bike is out of site, you need decent locking to make sure it doesn't get pinched. For an ugly bike a simple cable lock might be enough. If its a nice bike then the sky's the limit and you might need two D locks and a stout chainlock.
Things you should do for yourself:
- Store clean clothes and towel at work - a full change at least. Hang up your wet clothes somewhere to dry ready for the trip home.
- Get a decent waterproof jacket - you probably already have this given its the UK, but a waterproof jacket that can still breathe can be hard to find. You will sweat up the inside of a solid plastic coat. Ideally not a black coat for visibility reasons.
Depending on your weather you might want waterproof overtrousers too.
- Gloves - good for warmth, dryness, and abrasion resistance in a fall. Don't go expensive - they wear out as fast as cheaper ones. Full fingered will help too.
- Get decent lights - more important in winter/dark but there's also solid proof that daytime lights help too. Ideally should have two front and two rear so that if one dies you still have another working one.
- Get a waterproof bag to move things, whether it be your spare clothes, your phone, laptop, or whatever. Not just water-resistant. Then store some stout plastic bags inside for torrential days.
- Shoe covers. I haven't found a good answer here, but commuting in gumboots tucked up into overtrousers was an excellent way to keep the feet warm and dry. I've also tried overshoes but they're more for warmth not dryness. Your choice of pedal and shoe is relevant here.
Longer term, if there are problems then you may consider a smaller bike that can be folded and taken inside, and stored under your desk. Drawback is they're generally not great bikes, and can be expensive. Cheap folders tend to be heavy and no fun to ride, but are better than walking.
