Mumford has run the fund since 1988, but has worked in investment since the late 1960s. This means his career has taken in the "winter of discontent", the recessions of the Thatcher era and the EMU crisis in the 1990s, as well as more recent market crashes.
He says that his experience has taught him that buying at times of crisis is the best way to make money, although the best moment came shortly after the stock market crash of 2007.
"I think the opportunity now isn’t as big as it was in ‘07, as the big opportunities you get are when you are in a raging bear market and valuations fall out of the window and things get absurdly cheap," he said.
"On the one hand, things get cheap because people are scared stiff and risk-averse, and on the other hand you have some selling in the smaller companies end of the market."
"People will sell stocks that they can sell rather than the ones that they want to sell, because they will be stocks they can’t sell."
"I had a valuable lesson in ’73 when I was buying British Land at 10p to sell it later at £1.50."
However, the P/E ratio on the FTSE All Share is currently 14, and Mumford says this still represents a great opportunity.
"The market is no longer massively undervalued but it is still well below historical averages. The FTSE All Share long-term average has been about 16x and it has been as high as 30x."
"I could see it at 20x at some stage, which is a great opportunity."
Many investors retain a heavy weighting to bonds, as they are regarded as relatively low risk.
However, Mumford says that the returns on these instruments are so low that there is little point to investing in them.
"Why equities? What else is there? A client came to me the other day and asked me if he should put his money in a retail bond for 2015. The rate was 0.8 per cent, which means you are losing money with inflation."
"In the meantime, you are getting a decent yield from equities and at some stage the domestic economy will recover."
Many people who are investing for the long-term think that emerging markets offer the best opportunities.
However, data from FE Analytics suggests that those who took this attitude a few years ago could be regretting it.
The emerging markets index has performed disappointingly against the developed world markets over the past three years, making just 8.03 per cent while the FTSE All Share has grown by 31.83 per cent.
Performance of indices over 3yrs
Source: FE Analytics
While this is a lot less than the best-performing emerging markets funds have achieved, it does underline the danger of assuming that investing in certain markets is enough to ensure long-term success.
Mumford says that there are plenty of companies in the UK that have the potential to outgrow their market.
For those looking for long-term growth, he says that the beleaguered British high street banks could pay off.
"If you are prepared to have the risk involved and to take a five-year view, you will probably do pretty well out of the horrible banks like RBS and Lloyds," Mumford said.
"I have only about 1.5 per cent in each of those, and I think that’s an acceptable risk. Rather than some of the ones like HSBC where you might make 50 per cent, if you are lucky with these you could easily double your money in two or three years."
"The domestic insurers are another interesting area. A lot of shares have performed reasonably well."
"I am sure the two new companies will do well – Esure and Direct Line – and if you are looking for a recovery story, Aviva will be an interesting proposition."
Buying what is cheap is one of the hardest things for investors to do, because it means looking past all the negative news and commentary that has accompanied a stock on the way down.
However, Mumford says that experience has taught him to do this. He even thinks that investing in the battered property sector is a good long-term move, and there are few investors who would be brave enough to follow him there yet.
There are a couple of short-term factors that support investing in UK equities that Mumford says are under-appreciated.
The first is that pension funds have the least amount of their money in equities since the 1950s, and this will have to change, particularly in light of the strong run for bonds over the past few years, which is unlikely to continue.
"We are also at the start of the new tax year with the ISA and SIPP market," Mumford said.
"The AIM market will be more active in a year’s time because of the removal of stamp duty and AIM shares being made available in ISAs."
The manager says that when he talks to the management of companies in which he is thinking of investing, he senses growing optimism.
"Since Christmas, companies have almost to a man said things look a little bit better, whereas before they were very gloomy."
"I think things are a little bit better than they are saying, but they don’t want to say that at the moment."
The £83m Cavendish Opportunities fund, which has five FE Crowns, has more than doubled the returns of its FTSE Small Cap (ex IT) benchmark over five and 10 years, according to data from FE Analytics.
Over the past three years it has made 66.51 per cent compared with 41.85 per cent from the benchmark.
Performance of fund vs benchmark over 3yrs
Source: FE Analytics
The fund is available with a minimum initial investment of £2,500 and has ongoing charges of 1.58 per cent.