Yes you can, as long as you do not claim funding (thats from any UK government or student loans company) from both institutions. So you will have to pay for one of them yourself. Technically you could do a full year of open uni (120 credits) alongside your HND, if you can handle the workload.
Some university regulations will stipulate you cannot be registered to another institution at the same time, Open Uni do not have this so check with the other establishment.
Edit- Even if they did stipulate you cannot be registered with two institutions I doubt they would ever find out as long as you do not claim double funding.