I have a 10.5 hr layover in London heathrow. my big luggage will be checked through to my destination. However i will also have a backpack. Is it safe to leave that in the baggage storage if it has electronics(ipad, kindle)?

i have access to united club. Might i have access to this prior to leaving the airport, or will i be outside security after customs and need to re-enter to store luggage in the united club?