Notes for the young or nonBritish1. There were 20 shillings in one pound 2. There are 3 feet in one yard 3. When this was composed, a pound was a lot of money. A factory worker might have made ten pounds or less per week. I thought I had a solution, but a visitor to the site pointed out it was wrong (thanks, Allan). If you find a different solution, please let me know. To see the failed solution, click here. 

Across1. Total number of manhours worked by builders 4. Area of kitchen (square feet) 6 Cubic feet of earth required for terrace 7 Height of house above sea level 8 Length (feet) of the stone walling (= frontage + 5 x length of drive) 9 Length (feet) of side fence (= rear fence + 20 feet) 10 side of square kitchen (feet) 11 Side of square lawn (feet) 12 Frontage (Yards) 15 Cost (Pounds) of car 17 Amount (pounds) of legacy left after paying for car 20 Length of house (feet), which is a rectangle twice as long as it is wide. 21 Length of drive (feet) 22 Amount (pounds) of legacy left after paying for the house and before buying the car. 
Down1. Cubic yards of earth required for terrace (= length of footpath) 2 Area (square feet) of house (= 2 x area of lawn) 3 Number of hours each builder worked 4 Cost of house (shillings) 5 Cost of house (pounds) 7 Area of lawn (square feet) 9 Cost (shillings) of stone walling at 21 shillings/foot 13 Telephone number of house 14 Number of builders engaged on job 15 Length of drive + footpath + rear fence (feet) 16 Frontage (feet) 18 Number of doors in house 19 Number of windows (= 1.5 x number of doors) 