Personally, I'd find a long term savings account which offers you access at relatively short notice, for the time being. You are right that being a landlord can offer you some hassle - I've done that. If you don't get a tenant, it can be a millstone, and you still have to pay buildings maintenance and insurance.
Bring practical about it (and I don't want to sound pessimistic!), you and your new partner are a new couple, if it were me I'd want some financial security behind me - just in case. If you had a house and you let it, then needed the money, you might not be able to access the money for months.
You can put £5640 in a cash ISA before 5 April, the same amount (or more if it goes up) in a new ISA in 2014-15, so that'll give you tax free interest - then look for a longer term investment for the remaining £50K. That's what I'd do.