Just a thought here but you didnt make a profit of £450, that was your contribution to profit. In reality, and what a lot of people forget, is that you have overheads as well. You need to factor in the cost of paying for your van, diesel, insurance, road tax, servicing, mot, business insurance, tools, depreciation on tools equipment and van, phone costs, etc etc. Unless your van is paid for you probably have a weekly cost of £60 - £100 for all of that. More if like me you work in a larege rural area and do a lot of miles.i did the job over 2 weekends and a few evenings which hours wise made up about 6 , 8 hour days. i charged the customer £600,but spent £150 on materials so got £450 profit.
I worked mine out to £115. If your costs are similar then thats £335 you made before any tax and NI....... and don't say that you take cash and dont declare it. The black economy is a nightmare for quality tradespeople.