Whatever you can get away with for business purposes....not too many weekend trips though, they get a bit suspicious !

Avoid submitting receipts for Friday nights and on weekends. If they do investigate you - then they'll go through every receipt!

Not accounted for officially. Just that you end up paying more extra tax than you earn. Please note that I am not a tax expert - in fact it would be fair to say that I am pretty crap at taxes, but BF, I can let you know who I am using - let me know.

Meals during the week - taking clients out for meals
Christmas mail out (!)
Mileage (assuming you have a car) - there are limits though
Room rental - e.g. if you have 1 room out of 4, 1/4 of your rent can go towards it, however, you cannot claim electricity/heating bills.
Phone use - partial, but you can basically claim all calls during working hours
Internet - all of it
Train travel - again during the week, as others have said, avoid weekend stuff unless really legit
Computing equipment - obviously, although this is depreciated
Mobile telephony

You can also claim for travel to and from workplace, but that's a bit dubious if you are working from home.

Those are the ones I can think of off-hand, but it is worth speaking to a tax specialist at least once, then you just repeat year on year.

DINK is different to DINKY...

So you are on 150k x 2 = 300 k pa.

Sorry to be blunt, but IMO that's pretty (British understatement = very) good income (although I don't know anything about your situation re family etc.). If you are not saving much with this and driving your beamer (assuming that is what you want based on your post), then you need to look again at how you are spending your money.

You should be getting a slice of the pie to use your parlance. Maybe not as big a slice as you want, but still a slice.

I earn less that your combined income, but more than your single, supporting a family with 3 children and we are pretty comfortable TBH and enjoying our slice of cake.

Something tells me you're not telling the truth....