1. This might seem like a strange question to some, however I have never really known why I use washing up liquid.  It is just something I have always done because I grew up with it.  It gave me a sense of reassurance that things were cleaned ‘properly’ when cleaned with washing up liquid.  I have now found out the scientific explanation for using washing up liquid and the answer is below in the answer to Q.2.
2. Shop bought washing up liquids often say they contain anionic surfactants and non-ionic surfactants.  Surfactants are used in washing up liquid as they have two ends to them.  One is attracted to water and the other to dirt and grease.  When added to water and agitated they pull the dirt and grease from your dirty dishes into the water, making cleaning easier. 

   Other common ingredients in washing up liquids include fragrances and preservatives.  Some even claim to have antibacterial action.  For more information on what I think about antibacterial cleaners, have a look at my previous post: https://ecothriftyliving.com/wp3/?p=751. 

   The problem I have is that I don’t know which surfactants, fragrances and preservatives are being used in many cases and whether they are good, bad or ugly.  Ecover claims it’s product is biodegrable and has a ‘minimum impact on aquatic life’, however that means it is still having some impact and I’m not sure how happy I am with that.   

3. Washing up liquid prices range from around £1.30 a litre to over £4.00 a litre depending on the brand and where you shop.  The most expensive brand tends to be the well known ones and the cheapest, the shops own label.  There are various ‘eco’ versions on the market, some of which are as follows: Ecover washing up liquid, Eco Cleanhome washing up liquid, Tesco Naturally washing up liquid, Asda Eco Friendly washing up liquid.  Many of these tend to be at the cheaper end of the scale and are often cheaper than Ecover.  I haven’t tried other brands, so I don’t know if they are any good or not.
4. There are various recipes for washing up liquid out there.  Today I had a go at making my own, but it wasn’t great as I made it far too runny and it wasn’t very good at tackling grease.  I didn’t follow a recipe though, so that might be why it wasn’t great! I basically combined some of my liquid hand soap that I had already made (see my previous post http://ecothriftyliving.blogspot.com/2011/07/make-soap-at-home.html ), with some warm water and vinegar.  It could potentially be cheaper than shop bought washing up liquid and more eco-friendly if I do get it right, so I will continue to experiment!
5. Having experimented by making my own washing up liquid that wasn’t very effective, I realised that sometimes you do need more than water to effectively wash up, but it doesn’t have to mean using washing up liquid.  Scrubbing brushes, scouring pads and microfibre washing up cloths can be used instead.  
6. The way forward for me is to try microfiber washing up cloths, scrubbing brushes and scouring pads. I will do that first, as if they are successful, they should provide a significant financial saving compared to purchasing washing up liquid.  If they are not successful, I will experiment further with homemade washing up liquid and if that isn’t successful, I will resort to a cheaper brand of ‘eco’ washing up liquid.  I am going to keep my mind open to other alternatives however and I am going to investigate the issue of microfiber cloths and other cleaning implements a little further, as although they may be more environmentally friendly in some ways, they are entirely man made and I have no idea how eco-friendly their production is.

For more information about the science behind surfactants have a look at Science in the Box.