VanguardInvestor has a 0.15% platform fee. Not sure if that is the lowest on the market or not but it's probably pretty close to being the lowest. The downside is that they do not offer that many fund choices but when starting out that may be a good thing.
Fund charges will vary, as will performance. FTSE UK All Share Index Unit Trust Accumulation fund has a 7.88% annualised return over 5 years. This is a tracker fund, so it is designed to mirror what the market does, in this case the FTSE UK All Share.
Use tools like MorningStar Quick Rank to find the annualised return, then look at the information from the fund manager themselves. www.morningstar.co.uk/uk/fundquickrank/default.aspx
I would suggest you do a lot more research so that you understand more about how funds work and that you understand your risk level. Nothing is risk free... the market goes up and down.
I don't understand it myself yet, still learning. I recommend listening to the Meaningful Money podcast, that often covers issues relating to investing in the UK. He also has a book coming out next month, that may be useful. meaningfulmoney.tv/book/
As part of an investment strategy I feel that doing some investing yourself is fine. I put money into workplace pension (so someone else manages that), I put money into short term savings (so little interest but hardly any risk), I put money into some mutual funds within an ISA wrapper, plus I have property. So if you look at your overall wealth, your £5k may be quite a small amount and thus is something you can use to learn about how investing works.