My uni gave us the opportunity to switch into ChemEng after one year of NatSci, so I have a vague idea of what it entails (I picked the Chemistry route though!)
- Chemistry = lots of labs each week, more focus on the actual chemicals + reactions + mechanisms etc.
- ChemEng = hardly any labs, quite a lot of physics/ maths describing things like rates of reactions, flows of fluids around a plant, catalysts, etc.
If you really like Chemistry, do Chemistry - apparently there's very little of it in ChemEng (which is essentially engineering applied to Chemical applications). If you want to include more physics, consider a joint honors degree, or I would personally highly recommend Natural Sciences which gives you more flexibility.
Mind you, I'd point out that there is a fair amount of physics/ maths within chemistry - a chemistry degree is much more theoretical than the A level, you learn about things like bonding in molecules (and the horrible maths describing it), rate equations (LOTS of differential equations), etc. as well as the organic chemistry side (mechanisms, structures, etc.) and inorganic chemistry (stuff to do with metal ions forming complexes). Depending on what bits of physics you really enjoy, you may find that a fair amount of it is covered in a chemistry degree anyway, and some degrees give you the flexbility to pick one or two modules from other subjects too if you wanted to keep up a bit of physics but still do a chemistry degree rather than joint honours/ NatSci.