I'm not sure what you mean by 'vail pairs' of contact lenses.
Also note that many types of contact lens solution are relatively universal, and can be purchased at the destination. If you list the brand/type, someone can advise you if it can be easily purchased in the UK.
But checking TWO bottles of solution in your CHECKED luggage is absolutely no issue at all, nor am I sure why it would be an issue?
Are you planning on taking a travel size in your carry on luggage? If so, LHR does not permit sizes larger than 100ml in carry on luggage (unlike in the US where it falls under the medical exemption). But that is only an issue on your homeward journey, and if you post your brand, we can help you to find a 100ml bottle in the UK of your particular brand (or a viable substitute)