Did any British ever step foot in China before the 20th century?

read a flipping history book

Of course they did, trade has been consistant between the UK/China for centuries, well established in the early 1700s and most certainly before then...have a read of this British Museum paper http://www.britishmuseum.org/pdf/Chinese_trade.pdf

Hong Kong became a British Colony in 1846 so yes Britain stepped foot in China before the twentieth century.

English merchants have been in commercial contact with south Chinese ports since at least the 17th Century.

The British famously sent George Macartney to Beijing as an ambassador encouraging trade relations with the Qianlong Emperor during the late 18th Century.

The British Empire instigated the Opium Wars during the 19th Century which won them possession of Hong Kong up until 1997.

Yes Hong Kong was a British colony

Yes loads

Not really.