You could reply with something like:
£200 does sound low compared with the other quotes, especially if it includes cutting everything back, trimming the tree, and removing all the waste. however, if the quote is in writing and clearly states exactly what work is included, then that is the price you should expect to pay unless you agree to additional work. before they start, i would just confirm in writing that the £200 includes all labour, waste removal, and disposal costs, and ask whether there are any circumstances where the price could increase. some gardeners price aggressively to win work, particularly if they are building up reviews or can complete the job quickly. as long as they are insured, have good feedback, and the scope of work is clearly defined, i wouldn’t automatically assume there is a problem simply because they are cheaper than the others.