It looks like you have invalid form settings like the form action being address:
form action="Address:" If you don't want the page to forward, you can leave the action blank.
Also the name and id of inputs in the form, shouldn't have ":" or spaces in them, so Street: and Post Code are not good for these.
Another issue with your map is that your address you are using:
Unit 20, Shamrock Enterprises Centre, Wingate Road, Gosport, Hampshire, PO12 4DP, UK
If you input this into maps.google.com/ the address is not found. You will have to use an address that Google Maps recognizes for the map to display correctly. It appears that the issue is the street that you have put in:
Unit 20, Shamrock Enterprises Centre, Wingate Road
This cannot have commas in it, just the street number and the Street name.
Make those changes and give it a try.