Remember much of the FTSE 100's earnings (and hence much of UK listed companies, because the FTSE 100 is 80% of UK listed market cap or there abouts) comes from abroad. So even when you're buying 'UK', you aren't really (see: HSBC, Barclays, BP, all the mining companies, etc).
Not sure who you're with but have a look at Vanguard's offerings in the UK - they are generally cheaper. I don't know about Platform Fees and all that nonsense; I have ETFs (so, VWRL.L would be the equivalent), and use low fee options (iWeb Share Dealing for ISA, for example).
If you just want a single stock market 'thing' based on market weightings, what you selected and VWRL.L will do the same (I think), except the fund won't pay out dividends (it's an Accumulating fund) but the ETF will.
Buying 'the world' based on market cap is fine.
An alternative is the Vanguard LifeStrategy funds, which can include fixed income as well, all in a single package. So, LifeStrategy 60 for example is 60% stocks (with more UK stuff than the UK's market weight would generally suggest - this is called home country bias) and 40% bonds/gilts/treasuries.