I agree that the Jepp VFR charts are not perfect (some missing/incorrect information and sometimes slightly unclear as to precisely which bit of airspace starts at which height) but I much prefer them for VFR in France as the normal French charts only go up to 5,500' (or somewhere around there). However, having used both, I much prefer the UK CAA charts for UK VFR flying.
The IFR charts won't help a great deal for non-airways/uncontrolled airspace IMC flying (ie in the UK) however they will provide some useful information on frequencies that is not contained in the VFR charts. Given you can pick up the Jepp IFR charts for under £10 each, it's not bad to carry them.
Generally though, if you have an IMC rating (and not a full instrument rating), you'll be flying off (or beneath) airways and most likely in uncontrolled airspace. In those situations, the VFR chart is best to use as, absent one of those fancy new glass cockpit things, it is the only thing that will give you proper terrain information whilst enroute (although ideally you would also have a traffic or deconfliction service from an ATC unit - assuming you're not flying on a Sunday - which might assist if you get too low for safety).