For the Singapore Stock Exchange, the minimum lot size (number of shares) to trade is 1,000 units.
I was wondering: What is the minimum purchased unit for the London Stock Exchange?
Good question! It seems to me that there is no minimum order size for shares trading on the LSE. Please note, I couldn't find an definite answer, but:
According to the "International Order Book" document (see: http://www.londonstockexchange.com/traders-and-brokers/rules-regulations/change-and-updates/stock-exchange-notices/2010/n2210_attach1.pdf) from the LSE (page 7):
Question 7: Would respondents support a revision of the minimum order size of 50 units? Whilst there was limited support for a low value based minimum order size the majority of respondents requested its complete removal. This was incorporated into the September 2010 quarterly review as per Service Announcement 001/100910 and as from 20 September 2010, the minimum order size in all IOB securities has been 1 unit
Even though not all trading on the LSE is performed on this IOB system, it would be very wierd if the international stocks can be traded in any size, while domestic stocks will have an minimum size.
Further, consider looking to the times and sales of various stocks (here you can find an example http://www.londonstockexchange.com/exchange/prices-and-markets/stocks/exchange-insight/trade-data.html?page=0&fourWayKey=GB0006731235GBGBXSET1&formName=frmRow&upToRow=-1). Those trades also suggest that there is no minimum order size (for example, I just saw an executed trade with an size of 13).
At last, look at the Interactive Brokers (no relationship with) Exchange List at http://www.interactivebrokers.com/en/trading/exchanges.php?exch=lse&showcategories=&ib_entity=llc. Here you can click on various stock names, and in the popup window that opens, look for 'size parameters' and the size increment. I could only find stocks with an size increment of 1 (i.e. you can trade anything with a minimum of 1 stock, and more needs to be in steps of 1 stock).
Even though I couldn't find official information on the LSE site (like a leaflet for beginners or such), it does seem to me that you can trade any size you want on LSE.
Please note that mutual funds and illiquid OTC stocks which don't have an continuous market can have different rules, so double-check with your broker.
1 lot is 100 shares on London stock exchange