I'm from Saudi Arabia and I'm planning to visit UK next month but when I checked my visa it showed that it will expire in one month. So, Is it OK to make a journey in the last week of my visa? and make sure that I book my plane back before expiring date.
Yes it should be fine to visit the UK from Saudi Arabia the week before your visa expires. You must leave the UK by this date, unless you have successfully applied for permission to extend your stay. In some immigration categories, you cannot apply to extend your stay. They suggest that you apply for permission to extend your stay (if you are allowed to do so) at least 4 weeks before your visa's 'valid until' date. You can arrive in the UK at any time up until the 'valid until' date, but remember that this is also the last day that you are permitted to stay in the UK. Full details available here