The rush south of the Border follows Jet2 and Tui postponing the resumption of flights between Scotland and Spain because travellers will have to quarantine for two weeks after returning home.
This is because of Covid-19 levels in Spain, so it has been excluded from a list of 39 countries which Scots can visit without the need to quarantine from today.
The decision will be reviewed on 20 July.
English residents visiting Spain will not need to quarantine.
Jet2 has put back the resumption of its Spanish flights from Edinburgh and Glasgow from 15 to 25 July.
The Scottish Passenger Agents Association (SPAA), which represents many travel agents, said up to one in five of some of its members’ customers who had had their Spanish flights grounded had decided to fly from England instead.
The move comes despite First Minister Nicola Sturgeon warning travellers that Public Health Scotland could trace their movements even if they did not fly from Scotland.
This is because passengers arriving in the UK have to complete a form, with Border Force sharing information about those from Scotland with Public Health Scotland.
SPAA president Joanne Dooey said: "The news that Tui and Jet2 Holidays' flights to Spain have been cancelled for the forthcoming fortnight, which is usually one of the busiest in outbound travel terms, has been a huge blow to all of those booked on these flights.
"We find the decision to treat mainland Spain and its islands as one whole and to impose a blanket ban which excludes them from the ‘safe' travel list baffling.
"It is our understanding that the Balearic and Canary Islands have a very low infection rate, so it seems unfathomable why Scots can't travel to these islands.
"Many of the people booked on these flights have already had their holiday cancelled once and were re-booked for this fortnight.
"Many people will not want to re-book for a third time and all of this uncertainty increases the jeopardy which the Scottish outbound travel sector faces.
"Some Scottish agents have reported up to 20 per cent of their clients have opted to fly from Newcastle or Manchester airports when their Scottish flights were cancelled.
“Our members are all proactively pointing out to clients the quarantine requirements if they chose to change their flight from a Scottish departure airport to a flight from an English airport.
"However, it is up to individuals to comply with the Government policies on quarantine if they chose to travel.
"The main reaction to the quarantine advice is that clients listen and agree that they will do this, however, it is often with a wry smile.”
Ms Dooey added: "Our flight routes from Scottish airports are hugely valuable to the country.
"We're hearing a lot from the Scottish Government about supporting inbound tourism.
“Without outbound tourism, there can't be as much inbound tourism, so the outbound sector needs to be protected.”
Barrhead Travel, one of Scotland’s largest travel agents, said some of its customers were switching to English airports.
English airports ‘a viable option’
President Jacqueline Dobson said: “While holidaymakers are bound by law to respect the quarantine imposed by the Scottish Government, it is likely that many will still continue with their travel plans to Spain.
"There are a number of customers who have indicated they want to travel from an English airport to continue with their holiday as planned.
“The likes of Manchester and Newcastle airports are very accessible for Scottish holidaymakers and many are already considering the commute as a viable option if they cannot travel from Scotland.”
A Jet2 spokesperson said: “Because of the travel restrictions that are still in place to Spain as a result of this week’s announcement by the Scottish Government, we have taken the decision to recommence our flights and holidays programmes from Edinburgh and Glasgow airports to mainland Spain, the Balearic islands and the Canary islands on 25 July.
“We plan to resume our flights and holidays to other popular hotspots from Scotland on 15 July, and we will be announcing more details soon.”
Ms Sturgeon said on Wednesday: "You cannot get round the requirement to quarantine in Scotland by flying to or from an airport in England.
“Public Health Scotland will have access to contact details for people staying in Scotland, regardless of whether an individual arrives in Glasgow, Manchester or London and it will carry out sample checks."
Holidaymakers have given a mixed reaction to different quarantine restrictions in place in Scotland about travel to Spain, but are united in hoping the rules change before their return home.
Speaking at Edinburgh Airport, Roseann Campbell said she does not feel the divergence is fair, but she hopes for a change by the time she returns from her holiday in Malaga.
The 61-year-old, from Bathgate in West Lothian, said: “I don’t think it’s right if they lift it in one place but they don’t lift it here.
“But it’ll maybe change by the time I get back so I’ll be quite happy – I’m banking on it.
“It’ll not bother me, I’ll just stay in the house for two weeks.”
People returning or visiting from the 39 countries on the list with a low prevalence of Covid-19 – including Germany, Norway and Malta – no longer have to quarantine.
Other countries which have a lower or not significantly higher prevalence of the virus than Scotland – including France, Greece, the Netherlands, Italy and Poland – are also included.
Alison Watters, from Dunfermline in Fife, was also flying to Malaga today, for two weeks, but is comfortable with the potential of having to quarantine for 14 days.
She said: “I’m happy with it because I trust Nicola Sturgeon to have checked the figures.
“I’m hoping that by the time we get back it’ll be lifted but we work from home anyway.”
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