Hi Busy Bee!
Sorry you couldn't find a parking spot in Cambridge. Happy New Year anyway!
Different makes (and models) of TV reception devices (e.g. TV sets, digiboxes, dvd recorders, etc) have varying 'sensitivities'. This is their ability to 'pull in' and 'lock onto' weaker signals. If you've been getting good Freeview reception with a previous device, but not so with your new recorder, it almost certainly means that the sensitivity of the recorder isn't good enough to handle the signal it's receiving from your aerial. (Each channel is transmitted on a different frequency. Theoretically you should have a different aerial for every channel you watch, so that the aerial is always precisely 'matched' to the relevant frequency. That's obviously not practical, so all aerials will be slightly better at receiving some channels than others. Your aerial is obviously poorly matched to the BBC group of channels).
To receive the missing channels you need to increase the signal strength that the recorder is receiving. If you were previously getting a good enough signal (for a different device with slightly better sensitivity) it's quite likely that a simple signal booster will do the job. (They're fairly cheap. Try Tesco Extra, Asda or Maplin Electronics). Otherwise you'll have to upgrade your aerial system. (That means a new aerial and new cabling).
Chris